Patent Application
20080123755
The invention relates generally to data transmission apparatus and methods.
The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments of the present invention and together with the description serve to explain the principles of the invention. Other embodiments of the present invention and many of the intended advantages of the present invention will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.
a, 1b and 1c are diagrams illustrating embodiments of the invention.
a and 7b are diagrams illustrating embodiments of the invention.
a and 8b are block diagrams illustrating embodiments of the invention.
The following detailed description explains exemplary embodiments of the invention. The description is not to be taken in a limiting sense, and is made for the purpose of illustrating the general principles of embodiments of the invention. The scope of the invention, however, is defined by the claims and is not intended to be limited by the embodiments described herein.
The term “Data” as used to describe one or more embodiments of the invention is not limited to any specific data and may include for example voice data, multimedia data, text data, graphic data or other computer data.
The term “carrier” as used to describe one or more embodiments of the invention includes a tone or frequency sub-range of an equally or non-equally divided frequency range used for transmission of information on a transmission line. The term “carrier” might also be known in the art as sub carrier.
Modulation of information onto a carrier as used to describe one or more embodiments of the invention includes any assignment of information to this carrier to generate a signal comprising the information in any form within the signal. Modulation may for example comprise assignment to symbols, representatives of symbols or constellations. The assignment may use bitloadings and constellation vectors within a complex frequency domain. Modulation may according to embodiments of the present invention include QAM (Quadrature Amplitude Modulation), OFDM modulation (Orthogonal Frequency Division Multiplexing), DMT (Discrete Multi-tone) modulation, but is not limited thereto. 16 QAM (16 Quadrature Amplitude Modulation), QPSK (Quadrature Phase Shift Keying), DQPSK (Differential Quadrature Phase Shift Keying), BPSK (Binary Phase Shift Keying) or higher modulation schemes may be used for modulation.
“Transmission line” as used to describe one or more embodiments of the invention may be interpreted broadly and includes every physical transmission medium such as electrical lines, for example twisted pair lines, copper lines, coaxial lines or other physical lines.
“Band” as used to describe one or more embodiments of the invention includes a plurality of carrier grouped together which may be dependent on the specific standard used for transmission. The number of bands and whether they are used for transmission in both directions or in one direction (such as upstream and/or downstream) may depend on the specific standard used, for example VDSL, VDSL2, ADSL, ADSL+.
The term “xDSL” as used to describe one or more embodiments of the invention may be a synonym for all DSL-based techniques including but not limited to HDSL, HDSL2, ADSL, ADSL2, ADSL2+, VDSL, VDSL2, SDSL, IDSL, G.SHDL.
The term “symbol in the frequency domain” as used to describe one or more embodiments of the invention may refer to a vector or representative of a vector in the frequency domain corresponding to constellation points assigned to each of the carriers of a transmission system.
The term DMT-symbol or OFDM-symbol as used to describe one or more embodiments of the invention may refer to a signal in time domain generated after a frequency-to-time conversion of the symbol in the frequency domain which may comprise extensions such as a cyclic prefix or a cyclic suffix. The term DMT-symbol or OFDM-symbol as used to describe one or more embodiments of the invention may be sometimes referred to in the art as DMT-frame or OFDM-frame.
In the illustrated embodiments, transmission systems can include a first device or apparatus having a transmitter that transmits signals representing information along a transmission line that couples the first device and a second device to a receiver of the second device. In many transmission systems, the first device may not only be coupled to the second device but also to one or more other devices. In some embodiments, a plurality of transmission lines are coupled to the first device and the transmission lines may be in close proximity or in contact with each other, such as with a bundle of transmission lines. As a result, crosstalk of signals transmitted on one of the transmission lines to other transmission lines can effect transmission on one or more of the plurality of transmission lines.
a is a diagram illustrating one embodiment of cross coupling in a transmission system 100 that includes a plurality of transmission lines 102. The transmission system 100 comprises a first apparatus 200 having a plurality of N transceivers 110, wherein each transceiver 110 transmits and receives signals over one or more of the transmission lines 102, to the plurality of transceivers 104. The transceivers 104 may include in embodiments Customer Premises Equipment (CPE) such as a modem or router located for example at the home or office of subscribers of the transmission system 100. The apparatus 200 may be any transceiving unit. In one embodiment, the apparatus 200 is a Central Office (CO) such as the central office 150a, or is a cabinet 150b as shown in
b is a diagram of a transmission system 100a illustrating one embodiment of telephone lines. In the illustrated embodiment, the telephone lines comprise twisted pairs of copper lines that are used to transmit signals that can include xDSL or other suitable signals from the central office 150a to a plurality of modems 104a. The telephone lines connected to the central office are arranged at least over some distance in cable bundles 152 which may be connected to a cabinet 150b or directly connected to the modems 104a by splitting up the telephone lines of each cable bundle 152. Telephone lines connected between the cabinet 150b and the modems 104a may, in some embodiments, be aggregated in cable bundles which may be smaller than the cable bundles connected to central office 150a.
Referring to
In the illustrated embodiments, if a direct communication channel between receivers exist (e.g. the receiver devices are coordinated), crosstalk related to FEXT may be addressed by compensation at the receiver side. In embodiments of systems where no communication channel between the receiving devices exists, compensation of FEXT at the receiver side is difficult if information regarding the data transmitted on the other transmission lines is not available at the receiver side.
In one embodiment, in order to allow compensation of crosstalk related to FEXT, a technique known as precompensation (sometimes referred in the art also as preceding or precancellation) may be used at the transmitter side. With precompensation the effect of crosstalk experienced by a signal during transmission is computed or estimated prior to transmitting the signal and the signal is modified based on this information. In various embodiments, this can be performed by subtracting the calculated crosstalk from the transmission signal or by adding the inverse of the calculated crosstalk. During transmission when the transmission signal is exposed to the crosstalk, the transmission signal and the crosstalk are summed thereby resulting in the original or nearly original, i.e. unmodified or nearly unmodified signal, as provided at the transmitting side. In some embodiments, other noise may be added during transmission.
In the illustrated embodiments, computation of the crosstalk utilizes information related to signals transmitted on other transmission lines concurrently. In some embodiments, this information is available at the transmitter side as one or more devices may transmit on the transmission lines. The information related to signals on the transmission line may be derived from the data transmitted on the transmission line. In one embodiment, this is achieved by transferring information to a central controlling machine of the transmitting device.
In some embodiments, information related to the cross coupling of transmission lines, for example, to the percentage of power that is coupled from a first transmission line to a second transmission line, may be provided with the precompensation technique. In various embodiments, the information may include crosstalk channel estimates or other information including crosstalk coupling coefficients.
c illustrates a schematic view of one embodiment of precompensation at a transmitter side. As shown in
In various embodiments, a symbol in the frequency domain may be interpreted as a vector of constellation points for each of the carriers in the frequency domain spanned by real and imaginary axes corresponding to cosine-and sine functions. In other embodiments, other symbols for line coding may be provided by symbol generators 114 depending on the line coding used for transmission system 100. In the illustrated embodiment, each of the symbol generators 114 are coupled to frequency-to-time converters 106. In one embodiment, the frequency-to-time converters 106 are IFFT units (IFFT=Inverse Fast Fourier Transformation) that convert the symbols which represent a signal in a frequency space into signals in time space which are transmitted over transmission lines 102 to the receiver side. In the illustrated embodiment, between the plurality of symbol generators 114 and the plurality of frequency-to-time-converters 106, a precompensator 108 is provided to modify the symbols prior to converting same at the frequency-to-time converters 106. The precompensator 108 shown in
While the embodiment shown in
The compensation information used in embodiments of the precompensator 108, such as the compensation coefficients of the system illustrated in
According to embodiments of the invention, a signal is generated by a first apparatus or device, for example the CO or the cabinet illustrated in
In the illustrated embodiment, apparatus 300 comprises a terminal 302 configured to receive the first transmission signal, and comprises a machine 304 configured to generate information related to crosstalk on the transmission line during the transmission of the first transmission signal. In some embodiments, machine 304 generates the information related to crosstalk based on a comparison of second information related to the received first transmission signal with information based on the predetermined information. In the illustrated embodiment, apparatus 300 further comprises a modulator 306 coupled to the terminal 302 that generates and transmits a transmission signal. In one embodiment, this transmission signal represents the information related to crosstalk from the second device to the first device. In various embodiments, apparatus 300 may comprise a memory that stores full predetermined information, or may comprise a machine that generates the predetermined information based on reduced predetermined information which may be stored in a memory. In some embodiments, apparatus 300 comprises a feedback register or machine that simulates a feedback register generating information based on the stored reduced predetermined information.
In various embodiments, the transmission system 100 may be a xDSL system such as a VDSL, VDSL2, ADSL, ADSL2 or ADSL2+ system. In some embodiments, the carriers provided for transmission system 100 may be divided such that a first band or a first plurality of bands of the transmission system are used for transmission in one direction, for example from apparatus 200 to apparatus 300, and a second band or a plurality of second bands that are used for transmission in the opposite direction. According to one embodiment, apparatus 200 may be a CO or a cabinet, as shown in
According to one embodiment, the predetermined information may be information pre-known to each of the devices, for example pre-known information described in the transmission standard used by the transmission system. In some embodiments, contrary to systems using signals unknown to the receiver, the decision error introduced at the comparator on the receiving side can be exactly determined for pre-known information thereby eliminating any error in determining the information related to crosstalk which may be introduced when using a first signal based on known information unknown to the second apparatus 300.
In some embodiments, the predetermined information may be pseudo-random information, for example pseudo-random information generated by a feedback shift register. The predetermined information may be fully stored in a memory of apparatus 200 or only reduced information may be stored to generate the predetermined information by inputting the reduced information into a machine such as a processor or a feedback-shift register.
In some embodiments, the first signal represents a signal wherein all carriers provided for transmission from apparatus 200 to apparatus 300 are modulated by predetermined information. Thus, in the first signal, information carried by each of all carriers available for transmission from apparatus 200 to apparatus 300 is based on predetermined information and not user data. In other words, according to these embodiments, the predetermined information is transmitted by the first signal on all carriers available for transmission from apparatus 200 to apparatus 300 and no user data is contained within the first signal.
According to one embodiment, the predetermined information may be a predetermined DMT-symbol. According to one embodiment, the predetermined DMT-symbol may be a predetermined QPSK-symbol or a predetermined BPSK-symbol. QPSK-symbols and BPSK-symbols are low-bit symbols where each carrier is mapped only onto 2 bits (QPSK) or 1 bits (BPSK). According to one embodiment, the predetermined information may be a predetermined universal symbol of the transmission system provided for example according to a standard used by the transmission system for transmission. According to one embodiment, the predetermined information may be a control signal which is transmitted from apparatus 200 to apparatus to control at least one function of apparatus 300 based on the control signal. According to one embodiment, the control signal may be a synchronization signal controlling the starting of processes within apparatus 300 such as for example a VDSL 2 DMT-synchronization symbol. In come embodiments, combinations of one or more of the above described predetermined information may also be provided.
According to one embodiment, the controller may control the modulator such that the first signal is repeatedly generated based on predetermined information and transmitted over transmission line 102. One signal or a plurality of signals representing user data or data useful for a user, for example data requested by the user, may be provided and transmitted between each of the repeatedly transmitted first signals. The predetermined information may be the same for each of the repeatedly generated first signals. In one embodiment, different predetermined information may be used according to a predetermined switching scheme. For example, each of the repeatedly generated first signals may be mapped according to a predetermined scheme to at least one of a plurality of predetermined information.
In some embodiments, apparatus 200 may comprise a demodulator coupled to the terminal 204 to receive a plurality of transmission signals from the transmission line 102 and providing a plurality of information based on the plurality of received transmission signals. A selector may be coupled to the demodulator to identify the information related to crosstalk from the plurality of other information provided by the demodulator. Furthermore, apparatus 200 may comprise a machine to modify crosstalk precompensation information, for example precompensation coefficients, based on the identified information.
According to one embodiment, the modulator 202 may comprise a DMT-symbol generator encoding the first information onto a plurality of DMT-carriers and generating DMT-symbols. According to this embodiment, controller 208 controls the plurality of DMT-symbol generator such that at least one of the DMT-symbols is based on the predetermined information.
According to one embodiment, the modulator 202 generates the transmission signals based on encoding the plurality of information to a plurality of carriers of a transmission line according to a bitloading map. According to this embodiment, the controller 208 controls the modulator to generate the first signal independent of the bitloading map by using only QPSK modulation or BPSK modulation.
In some embodiments, the generation of the first signal which is provided for “testing” the cross coupling on a transmission line by using QPSK modulation provides a modulation wherein all constellation points of the signal have the same energy. This provides an improved convergence for training algorithms training the precompensation information for example during an initialization of apparatus 300.
In some embodiments, modifying and training of the precompensation coefficients may involve linear algorithms, non-linear algorithms or neural networking algorithms. In one embodiment, a singular value decomposition (SVD) technique may be used providing a diagonalization of the carrier matrix (channel matrix). In other embodiments, a Tomlinson-Harashima-basea crosstalk precompensator may be used as known in the art. Furthermore, in one embodiment, neural networks or neural network techniques may be used. In other embodiments, only partial crosstalk compensation may be provided. The partial crosstalk may be carrier selective (frequency selective), such that only selected carriers (tones) may be involved in precompensation based on the influence of these carriers to crosstalk. Furthermore, the partial crosstalk may be line selective, such that for a specific transmission line only selected carriers may be involved in providing precompensation taking into account that crosstalk may vary between different lines. Line selective crosstalk compensation is also known as space selective crosstalk compensation. Carrier-selective and Line-selective compensation may be combined in one embodiment. To implement the carrier- and line-selective compensation, Carrier- and Line-Algorithms may be provided selecting the carriers and Lines to be used in precompensation.
It is to be noted that embodiments of the present invention may be provided for all precompensation techniques based on a feed-back of information related to the crosstalk experienced by a transmitted signal from the receiver to the transmitter. Furthermore, embodiments may incorporate any training technique or adapting technique used for training or adapting precompensation values or precompensation coefficients.
In other words, the embodiments of the present invention may be used independent of a specific precompensation technique used for precompensation and independent of a training technique or an adapting technique used for training or adapting precompensation values.
According to one embodiment, apparatus 200 may comprise a plurality of further modulators coupled to a plurality of further transmission lines. A central controller may be provided controlling the transmission of signals on the transmission lines according to time slots. In specific, transmission of signals on the transmission lines is synchronized such that signals transmitted on one of the transmission lines and signals transmitted on the other of the transmission lines are provided in same time slots by the central controller. The central controller may provide data information related to data transmitted by the other transmitters within the time slot in which the first transmission signal generated based on predetermined information has been transmitted by one of the transmission lines. Crosstalk precompensation information such as crosstalk precompensation coefficients may then be modified based on the data information and the information related to crosstalk received from apparatus 300.
According to one embodiment, one or more carriers of the carriers provided for transmission from apparatus 300 to apparatus 200 may be exclusively or non-exclusively reserved for feeding the information related to crosstalk from apparatus 300 back to apparatus 200. In this embodiment, the demodulator of apparatus 200 may provide for each received signal a plurality of information associated with a respective one of the plurality of carriers of the transmission line, and the selector provided in apparatus 200 selects the information related to crosstalk based on the reserved carriers.
In various embodiments, the predetermined scheme used by selector 308 may provide a selection of every nth incoming signal. Selection may be based on the information contained within the first signal which may provide indication that the received signal is the first signal. Furthermore, the first signal may be contained within a frame or superframe, for example a VDSL 2 superframe, and the predetermined scheme may provide a selection of a specific symbol or range within the frame or superframe for example a specific numbers related to the position of the symbols within the frame or superframe. In one embodiment, the first signal is a DMT-symbol and every nth incoming DMT-symbol is selected by the selector.
In the illustrated embodiment, the first and second transceivers each transmit a plurality of signals over transmission lines 102-1 and 102-2, respectively. The controller 230 controls the transceivers 210 and 220 such that the first transceiver 210 transmits a specific first signal of the plurality of transmitted signals and the second transceiver 220 transmits a specific second signal of the plurality of transmitted signals transmitted by the second transceiver 220 time-shifted to each other. The first and second signals are received by apparatuses 300 and 400 and are identified by the respective selectors 308a and 408a using a predetermined scheme. According to one embodiment, the first and second signals are transmitted in a non-overlapping scheme. For example, the first signal may be transmitted within a first time-slot and the second signal may be transmitted within a second timeslot different than the first timeslot. Each of the apparatuses 300 and 400 may comprise a modulator or transmitter transmitting signals representing the information related to crosstalk back to the first apparatus 200. The first apparatus may comprise a precompensator providing precompensation to signals transmitted by the first and second transceivers 210 and 220 based on precompensation information and a machine modifying the precompensation information based on the signals transmitted back from each of the apparatuses.
It is to be noted that in various embodiments, the first and second information may be predetermined information as described above with respect to
According to one embodiment, the transmission may be a DMT-based system using DMT-modulation. The controller 230 may comprise a scheduler having a control circuit to time-shift the transmission of synchronization DMT-symbols, for example VDSL 2 synchronization DMT-symbols. In various embodiments, the scheduler may control transmission of the superframes such that a superframe transmitted over transmission line 102-1 is time-shifted with respect to a second superframe transmitted over transmission line 102-2. Since the synchronization DMT-symbols are provided always at the same position within the superframe, the time-shifted transmission of superframes results in a time-shift of the synchronization symbol.
It is to be noted that the embodiments described with respect to
a and 7b are diagrams that illustrate embodiments of the invention. According to one embodiment, superframes such as for example superframes as used by the VDSL 2 standard may be used for transmitting the signals over a plurality of transmission lines.
b illustrates an embodiment of scheduling of a plurality of superframes 600-0 to 600-24 for a plurality of 25 transmission lines. As can be seen in
According to above embodiment, the information related to crosstalk is only detected during the synchronization symbol providing a reduction of information related to crosstalk transmitted back to apparatus 200. Furthermore, since the synchronization symbol is a pre-known symbol, errors in the decision are eliminated resulting in an exact measurement of the information related to crosstalk.
The distribution of the synchronization symbols provides a more relaxed handling of the precompensation information. According to one embodiment, a precompensation algorithm of a precompensator provided by apparatus 200 may modify or adapt the precompensation information related to the different transmission lines one after another, thereby removing any workload peaks and distributing the workload over time.
It is to be noted that the above embodiments or parts of the described embodiments may be implemented by hardware, software, firmware or combinations thereof.
According to one embodiment, a computer program is provided which may be executed on a computing system and controls a first-VDSL-transceiver and a second VDSL-transceiver to transmit first synchronization DMT-symbols transmitted by the first VDSL-transceiver time-shifted to second synchronization DMT-symbols transmitted by the second VDSL-transceiver.
The computer program may control the transceivers described in
a and 8b are block diagrams illustrating embodiments of the invention.
In the illustrated embodiment, the hybrid circuit 816 receives an analog transmission signal from transmission line 102 and provides a digital representative of the received transmission signal via an analog-to-digital converter 818 to the demodulator 850. In specific, the output of the analog-to-digital converter 818 is coupled to an input of a second serial-to-parallel converter 820. The second serial-to-parallel converter 820 receives the digital signal and removes the cyclic prefix added to the signal. The outputs of the serial-to-parallel converter 820 are coupled to a plurality of inputs of a FFT time-to-frequency converter 822. The outputs of the FFT time-to-frequency converter 822 are coupled to frequency domain equalizers 823 which compensate the gain and the phase for each carrier. The output of the frequency domain equalizers are connected to comparators 824 for comparing each output signal representing a complex vector in frequency space with an expected vector in frequency space. The output of each of the comparator is connected to respective bit mappers 826 mapping the constellation vector to bit values. An input of a second parallel-to-serial converter 828 mapping the plurality of bit values received in parallel at the inputs to a single data stream at the output of the parallel-to-serial converter 828 according to a bit loading scheme.
In the illustrated embodiment, the output of the parallel-to-serial converter 828 is connected to a selector 830 separating the data related to crosstalk from other data. It is to be noted that various modification of the connection of selector 830 are possible. For example, the selector may be integrated within the parallel-to-serial converter 828 or the converter may be directly coupled to respective outputs of the bit mappers 826. The selector 830 is coupled at a first output to a data output providing the data transmitted on carriers other than the reserved carriers to a data output 834. The selector 830 is further coupled at a second output to a machine 842. The machine 842 modifies values of the precompensation information used by precompensator 808 for example as described with respect to
In the illustrated embodiment, memory 832 may also store information related to the indices of the carriers which is provided to the selector 830 for determining which data corresponding to the reserved carriers may be separated. Memory may, according to an embodiment, also be coupled to the data input 802 of each of transceivers to store the data transmitted by the transceivers. The controller 208 described with respect to the embodiments according to
b illustrates a further embodiment of the apparatus 300. As described above, input terminal 302 of apparatus 300 is provided for connection to the transmission line 102. A hybrid circuit 852 is connected to the terminal 302 for separating receiving and transmitting signals. A receiving signal is passed to an analog-to-digital converter 854 connected to a first serial-to-parallel converter 856. The serial-to-parallel converter 856 removes the cyclic extension and passes the received bits to a FFT time-to-frequency converter 858. Outputs of the FFT time-to-frequency converter 858 are coupled to a plurality of frequency domain equalizers 859. The output of the frequency domain equalizers are connected to a plurality of comparators 860 comparing the received data representing complex vectors in a frequency space to expected vectors. The plurality of comparators 860 are coupled to a plurality of bit mappers 862 mapping the vectors output by the FFT to respective bits. The plurality of bit mappers 862 are coupled to a parallel-to-serial converter 864 converting the parallel received bits to a serial data stream provided at a data output 866.
In embodiments of the transmission path of apparatus 300, a data input 868 of the modulator 306 is coupled to a second serial-to-parallel converter 870. The second serial-to-parallel converter 870 is coupled to a plurality of symbol generators 872 having outputs coupled to inputs of an IFFT-frequency-to-time converter 874. The outputs of the IFFT-frequency-to-time converter 874 are coupled to inputs of a second parallel-to-serial converter 876 adding a cyclic extension to the received parallel data and converting same to a serial data stream provided to an input of a D/A converter 878. The D/A converter 878 is coupled to the hybrid circuit 852 for transmitting the analog signal over transmission line 102.
In the embodiment shown in
While embodiments have been described with respect to apparatus 200 to have a plurality of transmitters or transceivers within one unit, it is to be noted that some or all of the plurality of transmitters may be located on a single chip or on different chips or within different housings which are coupled to transfer the information related to the data send over the plurality of transmission lines.
Furthermore, the functional units described with respect to the apparatus 300 or 400 may be provided on a single chip or on different chips.
Although the invention has been illustrated and described with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. In particular regard to the various functions performed by the above described components or structures (blocks, units, assemblies, devices, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component or structure which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the invention. In addition, any direct connection or coupling between two points, functional blocks, devices or other physical or functional units shown or described herein can be implemented by indirect connection or coupling including further elements or functional blocks in between. For example, one or more equalizers in time or frequency domain, interleavers, de-interleavers, scramblers, de-scramblers, filters, interfaces or drivers may be provided depending on requirements of specific embodiments. Furthermore, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”.
This application is related to an application having assignees Ref.No. 2006P52821US, filed Sep. 18, 2006, the contents of which are herein incorporated by reference in their entirety.
