Abstract: A method for selecting a mode of operation for at least two modems is described. First, a handshake procedure is performed in order to determine a set of possible modes of operation supported by said modems. From said set of possible modes of operation, a set of favorable modes of operation is derived. In case there exist two or more favorable modes of operation, a probing-based selection is performed that comprises evaluating respective performances of said favorable modes of operation. The favorable mode of operation with the best performance is selected as a resultant mode of operation.

Abstract: A method of optimizing a communication system for receiving and processing an input communication signal includes selecting a first noise margin m to be applied against an external noise present on the input communication signal. The method further includes selecting a second noise margin mi to be applied against an internal noise introduced on the communications signal by the communication system. The second noise margin is a predetermined function of the first noise margin. The method also includes calculating a virtual noise to signal ratio that is a combination of an external noise to signal ratio NSRe, an internal noise to signal ratio NSRi, the first noise margin and the second noise margin. The method further includes adjusting one or more system parameters so as to maintain the virtual noise to signal ratio at a predetermined margin above a required noise to signal ratio.

Abstract: The present invention provides systems and methods for pseudo-random signal generation in a multi-carrier communications system. In embodiments, a transmitter includes a pseudo-random bit sequence (PRBS) generator and Medley signal generator. The PRBS generator can operate in at least one of the following modes: a parameter selection mode, a scrambler mode, and/or a combination mode. The Medley signal generator receives an output bit sequence from the PRBS generator. The Medley signal generator then generates a Medley signal which includes a set of Medley tones encoded based on the output bit sequence from the PRBS generator. The Medley signal is then sent over channels of a multi-carrier communication system such as an ADSL system.

Abstract: A method to transport a reference clock signal from a central office to a line terminal in a communication system. The central office retrieves a reference clock signal, and a first counter in the central office is synchronized with the reference clock signal. The counter values of the first counter are regularly transferred as part of physical layer operation and maintenance cells over the optical link. A counter value of a second counter of the carrier unit is adjusted when a counter value is received as part of a physical layer operation and maintenance cell. Clock signals are derived from the second counter for the line terminal. The first counter values are inserted into a group of predefined message fields of the physical layer operation and maintenance cell, and extracted therefrom to adjust the value of the second counter.

Abstract: In a multi-carrier transmission system, a clock timing error (&tgr;e) is calculated at the receiver's side and used for synchronisation between a transmitting modem and a receiving modem (RX1). The clock timing error (&tgr;e) is calculated from phase errors (&phgr;0, &phgr;1, . . . , &phgr;i, . . . , &phgr;N-1) detected for a plurality of pilot carriers during a tracking mode in such a way that the share (Ai) of a phase error (&phgr;i) detected for a particular pilot carrier in the clock timing error (&tgr;e) depends on the transmission quality (SNRi) of that pilot carrier over the transmission medium in between the two modems. In this way, the robustness of the synchronisation for norrowband noise near a pilot carrier is improved significantly.

Abstract: The present invention provides a method for controlling transmission latency in a communications system, wherein the communications system is subject to a noise signal having at least a first noise phase and a second noise phase. The method includes determining a first bit rate for symbols transmitted during the first noise phase, and a second bit rate for symbols transmitted during the second noise phase, the first bit rate and the second bit rate being constrained such that a transmission latency does not exceed a pre-determined maximum allowed transmission latency; and transmitting symbols at the first bit rate during the first noise phase and at the second bit rate during the second noise phase. In other variants, the invention provides an apparatus, a constrained rate reciever, a transmitter and a signal.

Abstract: A technique for determining a symbol erasure threshold for a received communication signal containing symbol information is disclosed. The technique begins by performing a first threshold calculation to produce an initial symbol erasure threshold, then performing a first margin calculation to produce an initial symbol erasure margin and then modifying the initial symbol erasure threshold using the initial symbol erasure margin to produce a modified symbol erasure threshold. By then periodically modifying the modified symbol erasure threshold adaptive via updating the symbol erasure threshold and/or symbol erasure margin based on various error quantities, the technique can compensate for time-variant considerations, such as drifting noise levels.

Abstract: In a multi-carrier transmission system, a clock timing error (&tgr;e) is calculated at the receiver's side and used for synchronization between a transmitting modem and a receiving modem (RX1). The clock timing error (&tgr;e) is calculated from phase errors (&phgr;0, &phgr;1, . . . , &phgr;i, . . . , &phgr;N-1) detected for a plurality of pilot carriers during a tracking mode in such a way that the share (Ai) of a phase error (&phgr;i) detected for a particular pilot carrier in the clock timing error (&tgr;e) depends on the transmission quality (SNRi) of that pilot carrier over the transmission medium in between the two modems. In this way, the robustness of the synchronization for narrowband noise near a pilot carrier is improved significantly.

Abstract: Discrete multitone transmission assigns bits to tones for transmission. The bits are assigned using permutations of bits and tones that cycle through a sequence of permutations in successive frames.

Abstract: A time error compensation arrangement (TCOMP) that compensates for a time error (&egr;, &Dgr;k) between a transmitter sample clock in a multi-carrier transmitter and a receiver sample clock (CLK) in a multi-carrier receiver (RX1, RX2) includes a digital time correction filter (FILTER, FILTER′), operative in time domain, to compensate for a linearly increasing contribution (&Dgr;k) in the time error (&egr;, &Dgr;k) and rotation means (ROTOR), operative in frequency domain, to compensate for a second, remaining contribution (&egr;) in said time error (&egr;, &Dgr;k).

Abstract: A modem receiver 10 receives a multitone signal with a cyclic extension of M samples on a channel 20. The receiver includes a time domain equaliser 14 that includes a finite impulse response (FIR) filter. The FIR filter targets the combined response of the channel and filter to a target impulse response having N taps, where N is less than M+1.

Abstract: The invention relates to a reception arrangement for receiving multicarrier symbols, each multicarrier symbol (S1, S2, S3) comprising a plurality of single carrier symbols, each symbol modulating a respective carrier frequency (f1, f2, f3). The single carrier symbols are transmitted simultaneously. The arrangement comprises means for detecting phase error of each single carrier and means for correcting the phase of a sampling clock (52) in view of the estimated error.

Abstract: The present application describes a method to transport a reference clock signal (GPS) from a central office (CO) to a line terminal (LT1) in a communication system wherein the central office (CO) communicates with the line terminal (LT1) in a carrier unit (DLC) via an optical link (PON). The method comprises a) retrieving the reference clock signal (GPS) by the central office (CO); b) synchronizing a first counter into the central office (CO) with the reference clock signal (GPS); c) regularly transferring counter values of the first counter as part of physical layer operation and maintenance (PLOAM) cells over the optical link (PON); d) adjusting a counter value of a second counter of the carrier unit (DLC) when a counter value is received as part of a the physical layer operation and maintenance cell (PLOAM); e) deriving clock signals from the second counter for the line terminal (LT1).

Abstract: In a multi-carrier communication system wherein data are transferred bi-directionally in a time division duplexed way, a first pilot carrier is used to transfer a sample rate between two transceivers (VDSL_LT, VDSL_NT) and a second pilot carrier is used to transfer a time division duplexing frame rate between the two transceivers (VDSL_LT, VDSL_NT). The first pilot carrier has an instantaneous frequency that is a fraction of the sample rate of the first transceiver (VDSL_LT) and is orthogonal to other carriers used in the multi-carrier communication system. The second pilot carrier has a mean frequency that is a fraction of the time division duplexing frame rate and is also orthogonal to the other carriers used in the multi-carrier communication system. The second pilot carrier is different from the first pilot carrier.

Abstract: To determine the channel characteristic of a channel (CHANNEL) between a transmitter (TX) and a receiver (RX), a predetermined periodic signal of pulse amplitude modulated symbols is modulated on waveforms by a cosine modulated filter bank (DWMT MOD) in the transmitter (TX), and the waveforms are transmitted over the channel (CHANNEL). In the receiver (RX), the received pulse amplitude modulated symbols are demodulated from the waveforms by a cosine modulated filter bank (DWMT DEMOD), pairs of the received pulse amplitude modulated symbols are combined to form received quadrature amplitude modulated symbols, and the received quadrature amplitude modulated symbols are divided by the transmitted predetermined pulse amplitude modulated symbols considered pairwise as transmit quadrature amplitude modulated symbols. So, samples of the channel characteristic are generated.

Abstract: In a multi-carrier system, the carriers (f0 . . . f511, f512 . . . f1023, . . . , f3584 . . . f4095) are grouped in subsets (SUBSET1; SUBSET2; . . . ; SUBSET8). A constellation information transmitting arrangement (BiGi_TA), for instance located in the multi-carrier receiver (RX), produces for each carrier subset (SUBSET1; SUBSET2; . . . ; SUBSET8) a limited set of parameter values (B1, G1; B2, G2; . . . ; BG8) and transmits these sets of parameter values (B1, G1; B2, G2; . . . ; B8, G8) to a constellation information receiving arrangement (BiGi_RA), for instance located in the multi-carrier transmitter (TX). Through interpolation of the limited set of parameter values (BG1; B2, G2; . . . ; BG8) the latter constellation information receiving arrangement (BiGi_RA) determines the constellation where each carrier (f0 . . . f511, f512 . . . f1023, . . . , f3584 . . . f4095) of a carrier subset (SUBSET1; SUBSET2;. . . ; SUBSET8) will be modulated with.

Abstract: A triangular interleaver (INTERLEAVER) contains a triangular shaped matrix (MAT) of memory cells, each row of which constitutes a first-in-first-out queue. To increase or decrease the interleave depth of the interleaver (INTERLEAVER), the number of interleaved data bytes read from each row of the matrix (MAT) is positively or negatively linearly related to the ordinate number (0, 1, 2, 3, 4) of this row. In this way, impulse noise immunity of transmission of the outgoing interleaved data stream (OID) over a transmission line (TL) is kept substantially independent from transmit rate changes.