Abstract:
Method and device for data processing and communication system with such a device. The method and the device allow data processing via at least one channel. The method includes the following step of transmitting an idle pattern across the at least one channel when no information is conveyed. The idle pattern is created such that interference and/or crosstalk resulting from the idle pattern can be reduced at the receiving side.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a method and to a device for data processing and to a communication system comprising such a device. 
     DSL or xDSL, is a family of technologies that provide digital data transmission over the wires of a local telephone network. 
     Asymmetric Digital Subscriber Line (ADSL) is a form of DSL, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voice band modem can provide. Such fast transmission is achieved by utilizing frequencies that are normally not used by a voice telephone call, in particular, frequencies higher than normal human hearing. 
     VDSL (Very High Speed DSL) is an xDSL technology providing faster data transmission over a single twisted pair of wires. High bit rates are achieved at a range of about 300 meters (1000 ft), which allows for 26 Mbit/s with symmetric access or up to 52 Mbit/s in downstream −12 Mbit/s in upstream with asymmetric access. 
     Currently, standard VDSL uses up to 4 different frequency bands, two for upstream (from the client to the telecom provider) and two for downstream. The underlying modulation technique is DMT (discrete multitone modulation), wherein each tone carries a specified number of bits that are incorporated into a complex QAM (quadrature amplitude modulation) symbol. 
     According to its high bandwidth, VDSL is capable of supporting applications like HDTV, as well as telephone services (e.g., Voice over IP) and general Internet access, over a single connection. 
     VDSL2 (Very High Speed Digital Subscriber Line 2) is an access technology that exploits the existing infrastructure of copper wires that were originally used for plain old telephone service (POTS). It can be deployed from central offices, from fiber-fed cabinets preferably located near the customer premises, or within buildings. 
     VDSL2 is designed to support the wide deployment of Triple Play services such as voice, video, data, high definition television (HDTV) and interactive gaming. VDSL2 enables operators and carriers to gradually, flexibly, and cost efficiently upgrade existing xDSL infrastructure. 
     ITU-T G.993.2 (VDSL2) is an enhancement to G.993.1 (VDSL) that permits the transmission of asymmetric and symmetric (full duplex) aggregate data rates up to 200 Mbit/s on twisted pairs using a bandwidth up to 30 MHz. 
     The xDSL wide band modulation approaches are problematic relating to crosstalk interference that is introduced to the twisted pair transmission line and received by the modem. 
     Crosstalk occurs when wires are coupled, in particular between wire pairs of the same or a nearby bundle that are used for separate signal transmission. Hence, data signals from one or more sources can be superimposed on and contaminate a data signal. The crosstalk comprises a near-end crosstalk (NEXT) and a far-end crosstalk (FEXT). 
     Based on such crosstalk, data signals transmitted over twisted-pair lines can be considerably degraded by the crosstalk interference generated on one or more adjacent twisted-pair phone lines in the same and/or a nearby multi-core cable or bundle. With an increasing transmission speed, this problem even deteriorates, which may significantly limit a maximum data rate to be transmitted via a single line. 
     Furthermore, idle data sent induce crosstalk interference and hence disturb user data sent via other lines of, e.g., a multi-core cable. As there are typically 50 lines within one multi-core cable, such crosstalk could significantly impair the overall performance of the transmitting capability. 
     Processing of a pre-coding matrix at the central office (CO) results in processing a 50*50 matrix thereby consuming a significant region on a chip and leading to a high power consumption. 
     In order to support higher order modulation to increase data rate for the individual user and/or the total data rate transmitted from the central office to customer premises equipments (CPEs) inter-line cross-talk is a limiting factor for the achievable signal to interference and noise ratio (SINR) at the CPEs. 
     The main component of the inter-line crosstalk is determined by the coupling coefficients of the lines involved in the transmission system. The inter-line crosstalk is generally slowly varying over time and can be considered almost constant over a certain time period. 
     According to [1] achievable rates of a communication channel remain unchanged if the receiver observes the transmitted signal in the presence of additive interference, provided that the transmitter knows the interference non-causally. 
     It is known that for real time implementation on a dedicated hardware, sub-optimal schemes like Tomlinson-Harashima pre-coding for decentralized receivers (see [2], [4]) or joint transmission (see [3], [5]) can be used alternatively. 
     However, these concepts bear the disadvantage that an increased number of users results in a high complexity of the whole pre-coding procedure. Furthermore, it is almost a prerequisite that all user data have to be available in one processing unit, which would perform something like matrix vector multiplications on a per sub-carrier basis if DMT (Discrete Multitone Modulation) of OFDM (Orthogonal frequency-division multiplexing) is used as the underlying multi-carrier transmission technique. 
     DSL cables often contain twisted pair cables, where, e.g., five pairs are intertwined together as sub-cables and another ten of those sub-cables are twisted around each other to build the whole cable used in the field. Hence, relevant cross-talk happens inside each such sub-cable. 
     Such cable structure may enable an appropriate ordering of channel outputs (users) and channel inputs at the central office within the channel matrix thereby allowing a block structure in the matrix localizing the most relevant interference lines within such blocks of the channel matrix. 
     Such a structure of the channel matrix is a prerequisite for pre-coding which reduces inter-channel interference to a certain extent. However, if localization and hence clustering of the lines is not possible and hence a channel matrix comprising such a simplified block structure cannot be reached, the task of reducing interference between the lines may still be achieved, but at the expense of high complexity. 
     In a DSL environment, even if CPEs are not used and hence are not actively transmitting and/or receiving user data, still idle traffic is generated between each CPE connected and the CO or the DSLAM for, e.g., synchronization purposes. 
     Hence, the idle mode constantly generates interference and/or crosstalk with an impact to active lines conveying user data. 
     BRIEF SUMMARY OF THE INVENTION 
     The problem to be solved is to overcome the disadvantages as stated before and to reduce interference and/or crosstalk caused by network elements that are in an idle state as well as to reduce a complexity of pre-coding utilized for active (non-idle) users. 
     This problem is solved according to the features of the independent claims. Further embodiments result from the depending claims. 
     In order to overcome this problem, a method for data processing via at least one channel is provided comprising the following steps:
         transmitting an idle pattern across said at least one channel when no information is conveyed,   wherein said idle pattern is created such that interference and/or crosstalk resulting from said idle pattern can be reduced at the receiving side.       

     The at least one channel may connect a central office (CO) and/or a digital subscriber line access multiplexer (DSLAM) with at least one customer premises equipment (CPE). Information to be conveyed preferably relates to user data, e.g., video, voice, signaling, control, i.e. all kind of data that is different from idle data. Idle data, however, may not contain any information useful for or utilized by a subscriber. Idle data preferably relates to synchronization data for maintaining the connection itself. 
     The idle pattern is created in a way that allows a reduction of an interference and/or crosstalk resulting from said idle pattern. Said idle pattern may hence be chosen such that it can be compensated or reduced to a significant extent on the receiving side. In other words, the known idle pattern can be utilized on the transmitting side in a pre-coding process in order to achieve a benefit for compensation purposes (at the receiver) once the information and/or data is conveyed to the receiver. 
     Hence, the idle pattern may in particular be known to the receiver(s), in particular to the CPEs. This allows fast synchronization and interference reduction on the receiving side in particular during a setup phase. 
     A receiver at a CPE may listen to said idle pattern and hence synchronize on this idle pattern in a fast and efficient way. After synchronization, the receiver may request user data and is still able to further adapt its filters utilizing a difference between its user data and interference and/or crosstalk stemming from said idle patterns of at least one line of the cable binder. 
     In an embodiment, an identical idle pattern is conveyed for each channel. 
     In particular the identical idle pattern (that may further be chosen in a way to be compensated) can be used for at least two channels, in particular for all channels not transmitting user data (i.e. channels with associated network entities, e.g., CPEs, being in an idle state). 
     Hence, the idle pattern being the same for several channels allows to significantly reduce a processing effort for reducing an interference and/or crosstalk. 
     In another embodiment, information to be conveyed over the at least one channel is pre-processed such that interference and/or crosstalk can be reduced at the receiving side. 
     In a further embodiment, an active pre-coding is performed in particular at a central office for each channel that conveys information towards a customer premises equipment. 
     The central office (CO) may also be or comprise a digital subscriber access line multiplexer (DSLAM). Users are connected each to the CO by a customer premises equipment (CPE). Data is conveyed to the user (downlink) from the CO to the CPE. The opposite direction is referred to as uplink. 
     Pre-coding can be performed at the CO, in particular for each channel that has to convey user data to a CPE. Interference and/or crosstalk cancellation may then be processed at the CPE. 
     In a next embodiment, the at least one channel is at least one communication channel. In particular, the at least one channel may comprise at least one wireless channel. Alternatively or in addition, the at least one channel may comprise a fixed network channel. The at least one channel may also utilize WiMAX. 
     It is to be noted that the approach presented herewith does not only rely to the field of DSL, but also applies to various kinds of communication concepts via, e.g., fixed or wireless channels. Furthermore, combinations of wireless and fixed concepts may be utilized by the concept of data processing as suggested herewith. 
     It is also an embodiment that the at least one channel is at least one wireless and/or fixed connection between a central office and/or a digital subscriber line access multiplexer and at least one customer premises equipment at the receiving side. 
     Pursuant to another embodiment, the method provided is utilized in a communications network, in particular in a telecommunications network. 
     According to an embodiment, said at least one channel comprises at least one fixed point to multi-point connection. 
     According to another embodiment the fixed point to multi-point connection comprises at least one stationary or quasi-stationary positioning of a base station of a central office and/or of a user terminal. 
     The problem state supra is also solved by a device for data processing, in particular for interference and/or crosstalk reduction and/or cancellation comprising a processor unit that is arranged and/or equipped such that the method as described herein is executable on said processor. 
     It is an embodiment that said device is a communication device, in particular a Central Office (CO) or a Digital Subscriber Line Access Multiplexer (DSLAM). 
     According to a further embodiment, said device is a Customer Premises Equipment (CPE). In particular at the receiving side, a crosstalk and/or interference reduction (cancellation) may be performed utilizing the pre-coding conducted at the CO or DSLAM. 
     The problem is also solve by a communication system comprising said device as describe herein. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       Embodiments of the invention are shown and illustrated in the following figures: 
         FIG. 1  shows a schematic diagram comprising a transmission system with four transmitters and four receivers and a pre-coding block comprising an active pre-coding block; 
         FIG. 2  shows an equalizer structure at a receiver processing an incoming signal and reducing crosstalk and/or interference. 
     
    
    
     DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a schematic diagram comprising a transmission system with four transmitters and four receivers. 
     Data of different users, i.e. Data User 1  to Data User  4 , are input to a Pre-Coding Block  110 . Data User 1  and Data User 2  are in an idle state and convey no user data to the receiving side, whereas Data User 3  and Data User 4  are active and need to convey information to the receiving side, i.e. via transmitter Tx 3  to receiver Rx 3  and via transmitter Tx 4  to receiver Rx 4 . 
     Transmitters Tx 1  and Tx 2  (associated with Data User 1  and Data User 2 ) transmit idle patterns as they do not have to provide any “useful information” to their respective receivers Rx 1  and Rx 2 . 
     In order to allow an efficient pre-coding as well as significant interference and/or crosstalk reduction, identical idle data are transmitted via said transceivers Tx 1  and Tx 2 . 
     Due to crosstalk and/or interference, data conveyed via each channel/connection  114  to  117  may have a distinct impact to adjacent channels (shown by the dashed arrows in  FIG. 1 ). 
     Due to the identical idle patterns conveyed via channel  114  and channel  115 , an active pre-coding can be conducted for the channels  116  and  117  within the Pre-Coding Block  110 . 
     An Active Pre-Coding Block  111  allows to at least reduce crosstalk and/or interference arriving on a signal level  112  and  113  at the customer-premises equipments. 
     Due to the fact that identical idle pattern are conveyed via each channel (here  114  and  115 ) that does not have to transmit useful information, the idle pattern is known at the transmitter and can be considered within the active pre-coding. 
     The active pre-coding block  111  may further comprise pre-coding means to reduce a crosstalk/interference impact based on each of the transmitters Tx 3  and Tx 4  to the respective other channel  116  and  117 . 
       FIG. 2  shows an equalizer structure at a receiver. It visualizes as how signals  112  and  113  according to  FIG. 1  could be processed. 
     A signal  200  corresponds to the incoming signal  112  or  113  according to  FIG. 1 . Such signal  200  is preferably an input signal arriving at a customer premises equipment. 
     A block  201  depicts a receiver that may preferably include filters for processing the received signal. In particular, the block  201  comprises the elements required for processing the received signal on a carrier frequency. 
     Next, in a block  202  a cyclic prefix (CP) is removed and a FFT is conducted. 
     A subsequent block  203  comprises a frequency domain equalizer. The output of block  203  is fed to an adder  209 . 
     In a block  205  known data from an idle channel (see channels  114 ,  115  of  FIG. 1 ) is cancelled in a synchronized way from data symbols received. 
     The output of block  205  is fed to a block  206  which comprises an equalizer of idle data to subtract a sum interference of the joint interference channels of all idle users (idle channels, channels carrying idle pattern). A new filter matrix is determined by multiplying the old filter matrix with a residual filter matrix. 
     The output of block  206  is fed to the adder  209  and subtracted from the output signal of block  203 . 
     The result of the adder  209  is forwarded to a block  204 , i.e. a decision unit comprising a demodulator and a fault error correction (FEC) unit. 
     The output of block  204  is the output data stream for the user with cancelled (or at least reduced) crosstalk and/or interference. 
     The output of block  204  is also fed back to an adder  210 , i.e. subtracted from the input signal fed to the block  204 . 
     The output signal of the adder  210  is further fed to a block  207  performing an estimation of a residual idle channel and calculating compensation weights for interference and/or crosstalk cancellation based on known idle sequences including an optional interpolation in the frequency domain. 
     The output of block  207  is input to block  206 . 
     Hence, the approach presented herewith comprises in particular the following steps:
     a. All transmitters associated with users that are in an idle state convey the same sequence (idle pattern) to their respective receiver.
       Such a coherent transmission combines the interference channels of all idle users into a single transmission.   
       b. An interference/crosstalk suppression pre-coding is conducted for all active users that need to convey user data to their respective receivers.   c. Interference cancellation is conducted on the known idle sequence individually at each receiver using calculated weights utilizing a precise channel state information on the joint interference channel and appropriate weights.   d. The interference-cancelled data stream of the user is decoded using a suitable hard or soft decision de-mapper, preferably in combination with a forward error correction (FEC) code.   e. A residual interference is determined by subtracting a signal output by the hard or soft decision from a signal prior to such decision.   f. A known idle sequence is utilized to estimate the residual interference channel to update an interference cancellation filter. Further, frequency interpolations techniques may be used in order to reduce an estimation error.   

     Further advantages of the approach suggested are in particular as follows:
     (1) A significant interference and/or crosstalk reduction is achieved after cancellation at the receiving side.   (2) The interference channels of all idle users are combined into one channel and can be treated (processed) as one channel.   (3) This common and known interference based on the pre-defined idle pattern can be cancelled almost perfectly.   (4) The system is very robust.   (5) The system allows to smoothly follow the interference filter even in cases of (dis)connecting active users.   (6) Interference compensation may be completely performed at the terminal at a feasible and preferably fixed complexity.   (7) The system also compensates changes of the interference channel due to clock jitter between the transmitters and the receiving unit.   (8) The approach works dependent on a signal-to-noise ratio (SNR), i.e. the higher the SNR at a particular sub-carrier or sub-carrier block, the more important is an efficient interference suppression and the higher is the achievable gain in a throughput.   (9) Pre-coding on all active links may not be affected by the approach suggested and hence can be used for pre-transmission interference avoidance purposes.   (10) The complexity for the pre-coding is a function of the active users and not a function of all users which are connected and contribute to crosstalk.   

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