Abstract: Improved initialization techniques for initializing data transfer between a pair of transceivers in a multicarrier modulation transmission system are disclosed. The multicarrier modulation transmission system normally includes a central office and a remote unit, with the central office having at least one transceiver and the remote unit having a transceiver. For each pair of transceivers, the transceiver at either the central office or the remote unit controls the determining of bit allocations for both upstream and downstream data transmissions without assistance from the other transceiver of the pair. The initialization processing for the pair of transceivers is thus performed efficiently and with better centralized control.

Abstract: A method and apparatus for supporting multiple bit allocations in a multicarrier modulation system are disclosed. Hence, symbols being transmitted or received can make use of different bit allocations. By supporting the multiple bit allocations, the multicarrier modulation system is able to support bit allocation on a superframe basis. Also disclosed are techniques for selection and alignment of superframe formats to improve system performance.

Abstract: A discrete multitone modulation transmission system is described in which frame synchronization is monitored using a transmitted synchronizing frame. The existence or loss of frame synchronization is determined by comparing the values of the synchronizing frame with corresponding stored values.

Abstract: A transmission system includes transmit and receive paths coupled via a hybrid circuit to a bidirectional transmission path. The transmit path includes a digital-to-analog converter (DAC) having a given range and precision. The transmit path signal is limited and truncated to this range and precision before the DAC. In one arrangement including an echo canceller coupled between the transmit and receive paths, a difference of the transmit path signal before and after limiting and truncation is used to produce an estimated echo response which is subtracted from the receive path signal. In another arrangement, all of the inputs to the echo canceller are derived from the transmit path after the limiting and truncation. Instead, or in addition, the amplitudes of transmit path signal samples can be shaped in conjunction with the limiting. The system can in particular be an ADSL transmission system using multicarrier modulation.

Abstract: A discrete multitone modulation transmission system is described in which frame synchronization is monitored at the receiver by correlating frequency domain complex amplitudes of a synchronizing frame with a stored synchronizing pattern. If the correlation result falls below a threshold, indicating a loss of frame synchronization, a plurality of correlations are performed, in each case using the stored complex amplitudes of the synchronizing frame multiplied by a respective complex value representing a respective complex derotation corresponding to a respective possible time shift of the synchronizing frame. The best correlation result, if it exceeds another threshold, indicates a time shift for restoring frame synchronization, this being possible before the next synchronizing frame is received.

Abstract: A transmission system includes transmit and receive paths coupled via a hybrid circuit to a bidirectional transmission path. The transmit path includes a digital-to-analog converter (DAC) having a given range and precision. The transmit path signal is limited and truncated to this range and precision before the DAC. In one arrangement including an echo canceller coupled between the transmit and receive paths, a difference of the transmit path signal before and after limiting and truncation is used to produce an estimated echo response which is subtracted from the receive path signal. In another arrangement, all of the inputs to the echo canceller are derived from the transmit path after the limiting and truncation. Instead, or in addition, the amplitudes of transmit path signal samples can be shaped in conjunction with the limiting. The system can in particular be an ADSL transmission system using multicarrier modulation.