Signal processing arrangement and method for compensating or pre-compensating cross talk

Abstract

The invention relates to a signal processing arrangement (10) and a method for compensating or pre-compensating cross talk in a communication system (100) having M transmitters (Tx-1 - Tx-M) and N receivers (Rx-1 - Rx-N), the signal processing arrangement comprising a signal providing unit (2) configured to provide a first and a second set of digitized signals (HR1, HR2, LR3-LR6) based on at least some of the output signals (Rout-1 - Rout- 6) of the receivers or at least some of the input signals (In 1- In M) to be supplied to the transmitters (Tx-1 - Tx-M), wherein the digitized signals (HR1, HR2) of the first set of digitized signals have a higher resolution and / or sampling rate than the digitized signals (LR3-LR6) of the second set of digitized signals; and a MIMO processing unit (1) configured to receive the first and the second set of digitized signals (HR1, HR2, LR3-LR6) from the signal providing unit (2) and to process the first and the second set of digitized signals (HR1, HR2, LR3-LR6) to compensate or pre-compensate crosstalk.

Description

[0001] Signal processing arrangement and method for compensating or pre-compensating cross talk

[0002] Description

[0003] The invention relates to a signal processing arrangement according to claim 1 and signal processing method according to claim 16.

[0004] The exponential growth of data traffic in communication systems, e.g., optical communication systems, requires innovative strategies to increase the capacity of communication links. For example, coupled transmission channels, where multiple channels or modes are used simultaneously, offer a promising solution for significantly increasing throughput. However, channel coupling introduces crosstalk, a major impairment that degrades system performance. To mitigate crosstalk, which remains a major performance limiting factor, extensive multiple-input multiple-output (MIMO) processing is commonly employed. Despite its effectiveness, MIMO processing requires significant computational resources and poses challenges for processing large amounts of high-speed data in real time.

[0005] In scenarios with strongly coupled transmission channels, full MIMO processing is typically used to manage crosstalk between channels or modes. However, this approach is computationally intensive, making real-time implementation challenging. For example, a communication system may comprise M transmitters (Tx) to provide M transmitted channels are detected and digitized by N receiver frontends (Rx). A large-scale MIMO processor (MxN) may be employed at the receiver side for full crosstalk compensation. The MIMO processor may also be positioned before the transmission channel for pre-equalization. The complexity of MIMO processing may be reduced by employing several sub-processors assigned to sub-groups of the transmission channels as described in e.g., A. Gatto et al., "Partial-MIMO Based Mode-Group Transmission and Routing in a Field-Deployed 15-Mode Network: Throughput, DSP Resources and Network Flexibility", Journal of Lightwave Technology, vol. 42, no. 14, pp. 4720-4732, July 15, 2024. However, this concept ignores some of the crosstalk channels, which may lead to performance degradation.

[0006] It is an object of the invention to provide efficient crosstalk reduction while reducing processing complexity.

[0007] According to the invention, a signal processing arrangement for compensating (equalizing) or pre-compensating (pre-equalizing) crosstalk in a communication system having M transmitters and N receivers, is provided, the signal processing arrangement comprising

[0008] - a signal providing unit configured to provide a first and a second set of digitized signals based on at least some of the output signals of the receivers or at least some of the input signals to be supplied to the transmitters, wherein

[0009] - the digitized signals of the first set of digitized signals have a higher resolution and / or sampling rate than the digitized signals of the second set of digitized signals; and

[0010] - a MIMO processing unit configured to receive the first and the second set of digitized signals from the signal providing unit and to process the first and the second set of digitized signals to compensate or pre-compensate crosstalk.

[0011] Providing some of signals (the second set of digitized signals) to be processed by the MIMO processing unit with reduced resolution and / or sampling rate may reduce the processing demands and thus may allow a less complex design of the MIMO processing unit. The second set of digitized signals may be based on receiver signals or input signals that are related to crosstalk channels showing a weaker coupling to main transmission channels of the communication system, thereby allowing both take into account contributions of the weaker coupled crosstalk channel and reduce the processing complexity. In an MxM system (M transmitters and M receivers), each one of the transmitters may be assigned to a particular one of the receivers forming M main transmission paths (channels). Crosstalk channels are formed by transmission paths between a transmitter and the receivers not assigned to this transmitter. Some of these crosstalk channels (primary crosstalk channels) may have a greater impact on the signal transmission in the main transmission channels than other crosstalk channels (auxiliary cross talk channels) such that in order to take into account the crosstalk contribution of the auxiliary cross talk channels it may be sufficient to use the lower quality signals, i.e., the signals of the second set of digitized signals. The contribution of the primary crosstalk channels (or at least of some of the primary cross talk channels) and the main channels may be determined using the digitized signals of the first set of digitized signals, which have a higher resolution and / or sampling rate. Note that a “set” of digitized signals may consist of only one digitized signal. However, the first set of digitized signals comprises at least one signal and the second set of digitized signals comprises at least one signal. Accordingly, a hypothetical use a sampling rate of zero does not create signals of the second set. Further, more than two sets of digitized signals may be used, the sets being associated with different resolutions and / or sampling rates.

[0012] The signal providing unit may be configured to digitize the receiver signals, wherein the signals of some of the receivers are digitized using the higher resolution and / or sampling rate to create the first set of digitized signals and the signals of some others of the receivers are digitized using a lower resolution and / or sampling rate to create the second set of digitized signals. It is also possible that the second set of digitized signals is created by first digitizing signals of some of the receivers using the higher resolution and / or sampling rate and subsequently reducing the resolution and / or sampling rate. The first set of digitized signals may be provided by the signal providing unit based on a first group of the receiver output signals or the input signals to the transmitters and the second set of digitized signals may be provided by the signal providing unit based on a second group of the receiver output signals or the input signals to the transmitters. The first group and the second group may be mutually exclusive. It is, however, also possible that there is an overlap between the first and the second group. Also, it is not necessary that the signals of all of the receivers or all of the input signals to the transmitter have to be used by the signal providing unit.

[0013] The signal providing unit may be configured to receive analogue signals (the receiver signals or the input signals to the transmitters) and digitizes these signals. However, it is also possible that the signal providing unit receives digitals signals, wherein the digitized signals provided to MIMO processing unit are obtained by converting (e.g., by reducing the resolution and / or sampling rate) the received digital signal.

[0014] Moreover, the signal providing unit may comprise a sampler and a quantizer to digitize the receiver signals, wherein the digitized signals are supplied to the MIMO processor. The sampler may be separate from the quantizer. The resolution of the generated digitized signal is determined by the number of quantization levels provided by the quantizer. The sampling rate is the number of samples produced per unit time. Note that a signal “having” a higher resolution or sampling rate is to mean that the signals has been generated using a higher number of quantization levels and a higher sampling rate, respectively. The signal providing unit and the MIMO processing unit may be formed by a single device (e.g., a processor). However, at least parts of the signal providing unit may be separate from the MIMO processing unit, e.g., formed by a separate processor.

[0015] It is possible that the signal providing unit is a general digital signal processor. Further, the signal providing unit may process (digital or analogue) input signals to be supplied to the transmitters and provide the processed signals to the MIMO processor, which in this case may be configured for pre-compensation and feeds its output signals to the transmitters of the communication system.

[0016] The MIMO processing unit may be a specific electronic circuit (such as an ASIC) or may be realized by software running on a general-purpose computing device.

[0017] More particularly, the MIMO processing unit may comprise a first and a second group of (MIMO) filters to be applied to the digitized signals, wherein the filters of the first group are to be applied to the digitized signals of the first set of digitized signals and the filters of the second group are to be applied to the digitized signals of the second set of digitized signals. The MIMO filters may be digital filters (hardware or software filters), e.g., finite impulse response (FIR) filters. For example, the MIMO filters are associated with a filter weight matrix consisting of weight values representing characteristics of the filters. Each MIMO filter may be represented by one of the weight value of the filter weight matrix. The weight values belonging to the filters of the first group of filters may be above a pre-determined threshold, while the weight values belonging to the filters of the second group of filters may be below the threshold. Of course, more than two groups of filters corresponding to more than two sets of digitized signals may be present. The more than two groups of filters may be associated with different thresholds.

[0018] Each one of the weight values may represent an amplitude of an impulse response generated by the filter. The specifics of each one of the filters, e.g. its weight value, in turn, may be chosen depending on characteristics of one of the transmission channels (the main transmission channels and the crosstalk channels) associated with the filter. The characteristics of the transmission channels may be determined by channel estimation. A resolution reduction of the quantized input signals prior to applying (e.g., by multiplication) filters with small filter weights may conserve computational resources and may lead to a clear distinction between primary signal paths, which require higher resolution, and auxiliary paths, where reduced resolution is sufficient. According to another embodiment of the invention, the MIMO processing unit comprises at least a first and a second partition, wherein

[0019] - the first partition is configured to process the first and second set of digitized signals, and wherein

[0020] - the signal providing unit is configured to provide a third and fourth set of digitized signals based on output signals of the receivers or based on input signals to the transmitters and provide the third and fourth set of digitized signals to the second partition, the digitized signals of the third set of digitized signals having a higher resolution and / or sampling rate than the digitized signals of the fourth set digitized signals.

[0021] The first partition may be used to process signals transmitted via a first group of transmission channels, while the second partition may be used to process signals transmitted via a second group of transmission channels. For example, the first partition is used to reconstruct the signals transmitted by a first group of the transmitters or - in case of pre-compensation - to generate the signals to be transmitted by a first group of the transmitters. The second partition is used to reconstruct the signals transmitted by a second group of the transmitters and generate the signals to be transmitted by a second group of the transmitters, respectively (the second group being different from the first group). By means of the partitioning, the MIMO processing unit, for example, may only need to handle strong coupling between primary paths, while a weaker coupling to auxiliary paths can be accounted for with minimum computation effort and data exchange. Therefore, the partitions may be realized separately on different hardware parts. Further, the (e.g., partitioned) MIMO processing unit may be used for advanced optical transmission systems, such as those using few-mode fibers (FMFs) and multi-core fibers (MCFs), which may experience varying levels of crosstalk due to design or manufacturing variations. Moreover, the MIMO processing unit may be used for high-frequency wireless transmission in the millimeter-wave or terahertz range, where variable channel coupling can also occur. The partitioned MIMO processing unit may further reduce system complexity and power consumption compared to a full MIMO implementation, thereby lowering hardware demands. The partitioning may support the development of customized units tailored to specific channels or modes, providing scalability across various network architectures. By distributing the processing loads across multiple partitions (e.g., processors) the need for powerful and expensive hardware may be reduced.

[0022] The first and second partition may be connected to one another via an interface (hardware or software interface). For example, the second set of digitized signals is provided to the first partition from the second sub-processing via the interface and / or the fourth set of digitized signals is provided to the second partition from the first sub-processing via the interface. The interface may be configured to provide the second set of digitized signals and / or the fourth set of digitized signals. For example, the interface is configured to reduce the resolution and / or sampling rate of a digitized signal transmitted through the interface. That is, the signal providing unit may produce a digitized signal based on (from) a signal received from a receiver or a signal to be transmitted and may reduce the resolution and / or sampling rate of the digitized signal when transmitting the digitized signal through the interface. It is also possible that the interface generates the digitized signals of the second and / or fourth set (e.g., the interface comprises a quantizer and / or sampler).

[0023] The first and second partition may be formed by a first and a second sub-processing unit, which may be provided by separate processors. However, it is also possible that the first and second partition are formed by a single MIMO processor. Further, the MIMO processing unit may comprise more than two partitions.

[0024] The signal generating unit may comprise digitizing units forming part of frontends including the receivers, the digitizing units generating the digitized signals. However, the signal generating unit may also be separate to the receivers.

[0025] The invention also relates to a communication system comprising M transmitters for transmitting signals based on M input signals, N receivers to receive the signals transmitted by the M transmitters and a signal processing arrangement according to the invention. The communication system may be an optical communication system or a wireless communication system (e.g., a terahertz communication system comprising terahertz transmitters and receivers). For example, the optical communication system comprises a few-mode optical fiber, a multi-core optical fiber and / or a combined few-mode multi-core (FM-MCF) optical fiber for transmitting the transmitter signals to the receivers. However, the invention is not restricted to optical communication systems, but may be employed in other system, such as radio communication systems, as well.

[0026] Further, the invention is related to a signal processing method for compensating or pre-compensating crosstalk in a communication system, the communication system comprising M transmitters and N receivers, in particular using a signal processing arrangement as described above, the method comprising

[0027] - providing a first and a second set of digitized signals, the first and second set of digitized signals being based on output signals of the receivers or input signals to be supplied to the transmitters, wherein the digitized signals of the first set of digitized signals have a higher resolution and / or sampling rate than the digitized signals of the second set of digitized signals; and

[0028] - processing the provided first and a second set of digitized signals to compensate or precompensate crosstalk.

[0029] Embodiments of the invention will be described hereinafter with reference to the drawings, which show:

[0030] Fig. 1 an MxN communication system including MIMO processing;

[0031] Fig. 2 a basic layout of a MIMO processor;

[0032] Fig. 3A a cross section of a few mode fiber providing multiple transmission channels;

[0033] Fig. 3B a filter weight matrix related to the transmission channels provided by the few mode fiber of Fig. 3A;

[0034] Fig. 4 a signal processing arrangement according to a first embodiment of the invention;

[0035] Fig. 5 a signal processing arrangement according to a second embodiment of the invention;

[0036] Fig. 6 a modification of the second embodiment;

[0037] Fig. 7A a cross section of a multi-core fiber providing multiple transmission channels;

[0038] Fig. 7B a filter weight matrix related to the transmission channels provided by the multicore mode fiber of Fig. 7A; and

[0039] Fig. 8 a signal processing arrangement according to a third embodiment of the invention.

[0040] Fig. 1 depicts the basic design of an MxN communication system 100. The communication system 100 comprises M transmitters TX-1 - TX-M and N receivers Rx-1 - Rx-N for detecting signals generated by the transmitters TX-1 - TX-M. The signals generated by the transmitters TX-1 - TX (based on input signals ln-1 - In-M) are transmitted to the receivers Rx-1 - Rx-N via MxN transmission channels C including main transmission channels and crosstalk channels. For example, a main transmission channel may be formed between transmitter Tx-1 and receiver Rx-1, while crosstalk channels are formed between transmitter Tx-1 and the other receivers Rx-2 - Rx-N and between transmitters Tx-2 - Tx-M and receiver Rx-1. A MIMO processing unit in the form of a MIMO processor 1 is provided for crosstalk compensation. The MIMO processor 1 receives output signals Rout-1 - Rout-N created by the receivers Rx-1 - Rx-N and produces M compensated (equalized) output signals Out 1 - Out M based on the receiver signals Rout-1 - Rout-N. Accordingly, the MIMO processor 1 may comprise N input ports and M output ports. The output signals Out 1 - Out M are to correspond to the signals created and transmitted by the transmitters TX-1 - TX. The communication system 100 may be an optical communication system, a radio communication system or any other communication system. Further, the MIMO processor 1 may be arranged on the transmitter side, e.g., receiving the input signals ln-1 - In-M and generating and supplying pre-compensated signals to the transmitters TX-1 - TX.

[0041] Fig. 2 shows the basic layout of a MIMO processor 1 configured for compensation or precompensation in a 6x6 communication system (such as the one of Fig. 1 with M = N = 6). The MIMO processor 1 comprises a plurality of MIMO filters F11-F66 (e.g., FIR filters) depicted in a matrix representation. Each one of the MIMO filters F11-F66 receives one of the receiver signals Rout-1 - Rout-N (depending on the column of the matrix the MIMO filter is assigned to) and creates an output signal that contributes to the generation of one of the output signals Out 1 - Out 6 (depending of the row of the matrix the MIMO filter is assigned to). For example, MIMO filter F16 (first column, bottom row) receives the receiver output signal Rout-1 and contributes to the MIMO output signal Out 6. The other filters of the bottom row also contribute to the output signal Out 6 (similarly for the other rows, i.e., the output signals Out 1 - Out 5). For example, the individual output signals of the MIMO filters of one row may be summed to produce the output signal Out 1 - Out 6. Each one of the MIMO filters F11 -F66 may be associated with one of the transmission channels C of the communication system, wherein the filter properties may depend on the characteristics of the corresponding transmission channel. For example, the MIMO filters F11 , F22, ..., F66 positioned on the diagonal of the matrix representation are associated with the main transmission channels, while the other MIMO filters are associated with crosstalk channels. The principal layout of the 6x6 MIMO processor 1 shown in Fig. 2 may be transferred to an MxN MIMO processor used for an MxN communication system. Fig. 3A depicts a cross section of few mode fiber 20 used to provide transmission channels in an optical communication system. The few mode fiber 20 may be used in an MxN communication system 1 shown in Fig. 1 to provide at least some of the MxN transmission channels C. The few mode fiber 20 comprises a core 21 and a cladding 22, wherein the diameter of the core 21 is large enough to allow transmission of a plurality of (e.g., coupled) modes.

[0042] For example, the few mode fiber 20 may support six modes and thus may provide 6x6 transmission channels of a communication system. In such a system a 6x6 MIMO processor may be used for crosstalk compensation. Fig. 3B shows a filter weight matrix 11 assigned to such a 6x6 MIMO processor, the filter weight matrix 11 comprising weight values W11 - W66 representing characteristics (e.g., an amplitude of an impulse response) of the MIMO filters. The corresponding MIMO filters are shown in Fig. 4 and Fig. 5. The weight values W11, W22, ... W66 of the diagonal of the filter weight matrix 11 may belong to MIMO filters associated with the main transmission channels, while the other weight values belong to MIMO filters associated with crosstalk channels. The weight values W11 - W66 may be categorized into two (or more) categories depending on their values. For example, as shown in Fig. 3B, weight values below a predetermined threshold are depicted in grey, while weight values above the threshold are depicted in red. The MIMO filters depicted grey thus provide a smaller contribution when generating the MIMO processor output signals Out 1 - Out 6 than the MIMO filters in red (since the contribution of the crosstalk channels associated with the grey weight values is lower than the contribution of the transmission channels associated with the red weight values).

[0043] Fig. 4 depicts a signal processing arrangement 10 according to an embodiment of the invention and may be used for crosstalk compensation or pre-compensation in a communication system such as communication system 100 shown in Fig. 1, in particular using a few mode fiber as shown in Fig. 3A to provide the communication channels between the transmitters and the receivers. The signal processing arrangement 10 is related to a 6x6 communication system, the principal layout, however, could be used for an MxN system, i.e., a system having more or less transmission channels than the 6x6 system. The signal processing arrangement 10 comprises a MIMO processing unit in the form of a MIMO processor 1. The MIMO processor 1 comprises a plurality of MIMO filters F111-F66 (similarly to Fig. 2), the MIMO filters F11-F66 having weight values as shown in Fig. 3B.

[0044] The signal processing arrangement 10 further comprises a signal providing unit 2 having a sampler and quantizers Q. The signal providing unit 2 receives receivers signals Rout-1 - Rout-6 and provides a first and a second set of digitized signals to some of the MIMO filters (filters F11-F62, i.e., the filters of the first upper rows of the filter matrix). The first set of digitized signals comprises digitized signals HR1 , HR2 (depicted in red) generated based on receiver signals Rout-1, Rout-2, while the second set of digitized signals comprises digitized signals LR3-LR6 generated based on (depending on) receiver signals Rout-3 - Rout-6. The digitized signals HR1 , HR2 have been generated using a higher resolution and / or sampling rate than for the generation of the digitized signals LR3-LR6. The higher quality signals HR1 , HR2 are supplied to a first group of MIMO filters consisting of filters F11 , F21, F12, F22 (depicted in red) and processed by these filters, while the lower quality signals LR3-LR6 are supplied to a second group of MIMO filters consisting of filters F31-F62 (depicted in grey) and processed by these filters. The MIMO filters of the first group are associated with higher filter weights than the MIMO filters of the second group. That is, MIMO filters associated with lower filter weights, which correspond to crosstalk channels with lower impact on the main transmission channels, are supplied with signals of reduced quality (resolution and / or sampling rate), thereby taking into account also lower impact crosstalk channels but still reducing processing complexity as already mentioned above. Processing digitized signals HR1, HR2 and LR3-LR6 the MIMO processor 1 produces output signals Out 1 , Out 2.

[0045] The MIMO filters F11 - F62 of the upper two rows of the filter matrix form a first (6x2) partition P1 of the MIMO processor 1 generating output signals Out 1, Out 2. The MIMO processor 1 comprises a second (6x4) partition P2 comprising the MIMO filters of the lower four rows, i.e., MIMO filters F13 - F66, and producing output signals Out 3 - Out 6. The signal providing unit 2 provides a third and a fourth set of digitized signals to the second partition P2, the third set of digitized signals comprising high quality signals HR3 - HR6 generated based on receivers signals Rout-3 - Rout-6L and the fourth set of digitized signals comprising lower quality signals LR1 , LR2 generated based on receivers signals Rout-1 , Rout-2. The first and second partitions P1 , P2 may be realized by separate sub-processors.

[0046] Fig. 5 depicts a signal processing arrangement 10 according to a second embodiment of the invention based on a modification of the embodiment shown in Fig. 4. Similar to the embodiment of Fig. 4, the signal processing arrangement 10 according to the second embodiment may be used in conjunction with a communication system having transmission channels realized by a few mode fiber. As shown in Fig. 5, the MIMO processor 1 comprises a first (6x2) partition P1 and a second (6x4) partition P2 corresponding to the first and second partition shown in Fig. 4. Also similar to Fig. 4, the signal providing unit 2 supplies high quality digitized signals HR1 , HR2 and low quality digitized signals LR3-LR6 to the first partition P1, i.e., to MIMO filters F11-F62, and high quality digitized signals HR3-HR6 and low quality digitized signals LR1 , LR2 to the second partition P2, i.e., to MIMO filters F13-F66. The first and second partition P1 , P2 are connected to one another by an interface 200 of the signal providing unit 2. The interface 200 is a low resolution and / or low sampling rate interface and is used to provide the low quality signals LR3-LR6 from the second partition P2 to the first partition P1 and the low quality signals LR1 , LR2 from the first partition P1 to the second partition P2. More particularly, the signal providing unit 2 may first generate high quality digitized signals based on the receivers signals Rout-3 - Rout-6 and Rout-1 , Rout-2 (using high resolution quantizers HQ1 -HQ6), wherein the high quality signals are converted into the lower quality signals LR3-LR6 and LR1 , LR2 by means of low resolution quantizers LQ1-LQ6), respectively. The low resolution quantizers LQ1-LQ6 may be part of the interface 200. Further, as shown in Fig. 6, instead of using the high resolution quantizers HQ1-HQ6 and the low resolution quantizers LQ1-LQ6 successively to generate the lower quality signals LR3-LR6 and LR1, LR2, respectively, the receiver signals Rout-1 - Rout-6 may be digitized directly (in parallel) both by the low resolution quantizers LQ1-LQ6 and the high resolution quantizers HQ1-HQ6 to generate the high and low quality signals. Again, the low resolution quantizers LQ1 -LQ6 may be part of the interface 200. Note that the quantizers HQ1-HQ6 and LQ1-LQ6 may be combined with corresponding samplers.

[0047] Fig. 7A depicts the cross section of a (e.g., weakly coupled) multi-core fiber 30 used to provide transmission channels in an optical communication system (such as the MxN communication system 1 of Fig. 1). The multi-core fiber 30 comprises multiple (six) cores 31 embedded in a common cladding 32 and arranged in a hexagonal pattern. The multiple cores 31 provide multiple transmission channels. In particular, six main transmission channels may be provided by the six cores besides cross talk channels representing crosstalk between the cores 31 (resulting in 6x6 transmission channels). Of course, multi-core fibers having more or less than six cores may be used.

[0048] Fig. 7B shows a filter weight matrix 11 assigned to a 6x6 MIMO processor used to compensate crosstalk between the multiple cores of the multi-core fiber 30 shown in Fig. 7A. The filter weight matrix 11 similarly to the matrix shown in Fig. 3B comprises weight values W11 - W66 representing characteristics (e.g., an amplitude of an impulse response) of the MIMO filters of the MIMO processor. The corresponding MIMO filters are shown in Fig. 8. The weight values W11 , W22, ... W66, of the diagonal of the filter weight matrix 11 may belong to MIMO filters associated with the main transmission channels provided by the cores 31 of fiber 30, while the other weight values belong to MIMO filters associated with crosstalk channels, i.e., signals paths between different cores of the fiber 30. The weight values W11 - W66 are categorized into three categories depending on their values. The diagonal values W11 , W22, ..., W66 com- prise the highest weight values (red), wherein the other matrix elements represent low or essentially zero weight values (white) and weight values (grey) between zero and the highest values, respectively. The white and grey weight values correspond to cross talk channels existing between adjacent cores of the multi-core fiber.

[0049] Fig. 8 shows a signal processing arrangement 10 according to another embodiment of the invention and may be used for crosstalk compensation or pre-compensation in a communication system using the multi-core fiber 30 of Fig. 7A to provide the communication channels between the transmitters and the receivers. The signal processing arrangement 10 comprises a MIMO processor 1 and a digital signal providing unit 2 similarly to the signal processing arrangements 10 shown in Fig. 4 to 6 The MIMO processor 1 comprises multiple MIMO filters, wherein, however, crosstalk channels having a low (or essentially zero) contribution are ignored (indicated by the white squares in Fig. 7B) so that each row of the filter matrix is depicted to comprise only three MIMO filters. Each row of the filter matrix may form a partition P1-P6 of the MIMO processor 1 , wherein at least some of the partitions may be formed by separate subprocessors. Each partition generates one of the output signals Out 1 - Out 6.

[0050] The digital signal providing unit 2 provides one high quality digitized signal HR1 (red) and two low quality digitized signals LR2 and LR6 (grey) to the MIMO filters F11, F22 and F61 of the first partition P1 . Similarly, one high quality signal (red) and two lower quality signals (grey) are transmitted to the MIMO filters of the other partitions P2-P6. Note that it is also possible that the MIMO processor 1 comprises less partitions or no partition at all. Further, interfaces may be provided between the partitions P1-P6 as shown in Fig. 5 and 6, the interfaces providing the lower quality signals.

Claims

Claims1. A signal processing arrangement (10) for compensating or pre-compensating cross talk in a communication system (100) having M transmitters (Tx-1 - Tx-M) and N receivers (Rx- 1 - Rx-N), the signal processing arrangement (10) comprising- a signal providing unit (2) configured to provide a first and a second set of digitized signals (HR1, HR2, LR3-LR6) based on at least some of the output signals (Rout-1 - Rout- 6) of the receivers or at least some of the input signals (In 1 - In M) to be supplied to the transmitters (Tx-1 - Tx-M), wherein- the digitized signals (HR1 , HR2) of the first set of digitized signals have a higher resolution and / or sampling rate than the digitized signals (LR3-LR6) of the second set of digitized signals; and- a MIMO processing unit (1) configured to receive the first and the second set of digitized signals (HR1 , HR2, LR3-LR6) from the signal providing unit (2) and to process the first and the second set of digitized signals (HR1 , HR2, LR3-LR6) to compensate or pre-compensate crosstalk.

2. The signal processing arrangement as claimed in claim 1 , wherein the MIMO processing unit (1) comprises a first and a second group of filters (F11-F62) to be applied to the digitized signals (HR1 , HR2, LR3-LR6), wherein the filters (F11-F22) of the first group are to be applied to the digitized signals (HR1 , HR2) of the first set of digitized signals and the filters (F31-F62) of the second group are to be applied to the digitized signals (LR3-LR6) of the second set of digitized signals.

3. The signal processing arrangement as claimed in claim 2, wherein the filters (F11-F62) are associated with a filter weight matrix (11) consisting of weight values (W11-W62) representing characteristics of the filters (F11-F62), wherein the weight values (W11-W22) belonging to the filters (F11-F22) of the first group of filters are above a pre-determined threshold, while the weight values (W31-W62) belonging to the filters (F31-F62) of the second group of filters are below the threshold.

4. The signal processing arrangement as claimed in any of the claims, wherein the MIMO processing unit (1 ) comprises at least a first and a second partition (P1 , P2), wherein - the first partition (P1 ) is configured to process the first and second set of digitized signals (HR1 , HR2, LR3-LR6), and wherein- the signal providing unit (2) is configured to provide a third and fourth set of digitized signals based on output signals (Rout-1 - Rout-6)of the receivers or based on inputsignals to the transmitters and provide the third and fourth set of digitized signals (HR3- HR6, LR1 , LR2) to the second partition (P2), the digitized signals (HR3-HR6) of the third set of digitized signals having a higher resolution and / or sampling rate than the digitized signals of the fourth set (LR1 , LR2) of digitized signals.

5. The signal processing arrangement as claimed in claim 4, wherein the first and second partition (P1 , P2) are connected to one another via an interface (200).

6. The signal processing arrangement as claimed in claim 5, wherein the second set (LR3- LR6) of digitized signals is provided to the first partition (P1) from the second partition (P2) via the interface (200) and / or the fourth set (LR1, LR2) of digitized signals is provided to the second partition (P2) from the first partition (P1) via the interface (200).

7. The signal processing arrangement as claimed in claim 5 or 6, wherein the interface (200) is configured to provide the second set of digitized signals (LR3-LR6) and / or the fourth set of digitized signals (LR1 , LR2).

8. The signal processing arrangement as claimed in any of claims 4 to 7, wherein the first and second partition (P1 , P2) are formed as separate processors.

9. The signal processing arrangement as claimed in any of claims 4 to 7, wherein the first and second partition (P1 , P2) are formed by a single processor.

10. The signal processing arrangement as claimed in any of claims 4 to 9, wherein the MIMO processing unit (1) comprises more than two partitions, each one of the partitions generating at least one output signal of the MIMO processing unit (1).11 . The signal processing arrangement as claimed in any of the preceding claims, wherein the signal providing unit (2) comprises digitizing units forming part of frontends including the receivers (Rx-1 - Rx-N).

12. A communication system (100) comprising M transmitters (Tx-1 - Tx-M) for transmitting signals based on M input signals (In 1- In M), N receivers (Rx-1 - Rx-N) to receive the signals transmitted by the M transmitters (Tx-1 - Tx-M) and a signal processing arrangement (10) as claimed in any of the preceding claims.

13. The communication system as claimed in claim 12, wherein the communication system (100) is an optical communication system.

14. The communication system as claimed in claim 13 further comprising a few-mode optical fiber (20), a multi-core optical fiber (30) and / or a combined few-mode multi-core optical fiber for transmitting the transmitter signals to the receivers (Rx-1 - Rx-N).

15. The communication system as claimed in claim 12, wherein the communication system (100) is a wireless communication system.

16. A signal processing method for compensating or pre-compensating crosstalk in a communication system (100), the communication system (100) comprising M transmitters (Tx-1 - Tx-M) and N receivers (Rx-1 - Rx-N), in particular using a signal processing arrangement (10) as claimed in any of claims 1 to 11 , the method comprising- providing a first and a second set of digitized signals (HR1, HR2, LR3-LR6), the first and second set of digitized signals (HR1, HR2, LR3-LR6) based on output signals (Rout-1 - Rout- 6) of the receivers or input signals (In 1- In M) to be supplied to the transmitters (Tx-1 - Tx-M), wherein the digitized signals of the first set (HR1 , HR2) of digitized signals have a higher resolution and / or sampling rate than the digitized signals of the second set (LR3-LR6) of digitized signals; and- processing the provided first and a second set of digitized signals (HR1 , HR2, LR3- LR6) to compensate or pre-compensate crosstalk.

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