Abstract: The startup, retrain, renegotiation quick connect or other processes of handshaking between communication systems involve the exchange of certain modulation, constellation, precoder, prefilter and other communication related information. The communication systems exchange one long information sequence including all the necessary communication information. Subsequently, the communication systems start transmitting short sequences, including an acknowledgement information portion. If one of the communication systems does not receive an acknowledgement within a predetermined time or event, that communication system may retransmit another long information sequence. After such retransmission, the retransmitting communication system may continue transmitting the long information sequences or may start transmitting the short sequences once again. Eventually, each of the communication systems should receive a long information sequence and acknowledge their receipt of such sequence.

Abstract: A system, method, and signal are disclosed for line probing. The invention provides an improved signal for line probing having desirable characteristics. In various embodiments the signal comprises a periodic sequence having good autocorrelation characteristics. The periodic sequence of the invention provides a faster and more accurate evaluation of the channel. Another embodiment of the invention comprises processing of the received sequence to determine a desired or maximum data rate for the line or channel. The invention also provides an evaluation and calculation of the noise on the line or channel.

Abstract: A tone predictor may be employed in a modem system to cancel periodic interference components present in a received signal. The tone predictor may be implemented in a receiver arrangement to cancel such periodic interference and to condition a decision error signal utilized to update the adaptive equalizers. The tone predictor may also be implemented in an echo canceler arrangement to cancel such periodic interference and to condition the error signal used to update the echo canceler filter. The tone predictor includes a delay element, configured to decouple the periodic interference component from other noise components, and an adaptive filter structure configured to generate a periodic interference estimate.

Abstract: A modem system having two modem devices digitally connected to a digital telephone network includes an inband control signal channel. The inband control signal channel is formed by using the most significant bit position of every sixth transmitted codeword for the transmission of control data. The control signal includes a predetermined header section that is monitored by the receiving modem to maintain frame synchronization and to correct for digital frame slippage. The control signal also includes a number of control data packets that contain information related to the initiation of control procedures such as rate renegotiations and retraining requests. The disclosed inband transmission techniques may additionally (or alternatively) be utilized to define a secondary data channel.

Abstract: A preferred timing recovery scheme is particularly suitable for a high speed digital data communication system that employs T-spaced equalization in the receiving device, where echo cancellation occurs after equalization. The timing recovery technique is based upon an analysis of the impulse response of the equalizer structure (e.g., a structure having a feedforward equalizer and a decision feedback equalizer). The filter tap coefficients of the equalizer elements are analyzed and the sampling phase is adjusted such that a cost function associated with the performance of the equalizer structure is substantially optimized. The sampling phase of the receiver is adjusted in response to a control signal generated as a result of the timing recovery techniques.

Abstract: A modem system utilizes PCM encoding and transmission techniques in the upstream direction from a client modem (connected to a digital network via an analog loop) to a central site modem (connected to the digital network via a digital link). The modem system employs precoding techniques that enable the transmit signal to be pre-equalized to compensate for the analog channel characteristics. The precoding technique generates a plurality of equivalent signal point sequences in response to a digital data input. The signal point sequences are analyzed and compared relative to a predetermined cost metric such as transmit power. A preferred signal point sequence is selected and transmitted to the central site modem.

Abstract: A pulse code modulation modem system utilizes the same total average transmit power formula for designing signal point constellations and for verifying that the transmit power of the signal point constellations are within a designated maximum power limit. The transmit power of the signal point constellations designed by the client modem is also calculated by the server modem to verify that the transmit power limit imposed upon the server modem is not exceeded. In addition, the modem system is capable of designating a transmit power limit associated with one or more training signal points or a training sequence for use during a training mode.

Abstract: A modem system includes a programmable synchronization signal format that can be configured at a first modem in response to a request received from a second modem. The synchronization signal format may define a number of parameters of the synchronization signal, such as the sign pattern for symbols transmitted by the first modem during a training sequence. The specific parameters of the synchronization signal format may be associated with the design and operation of the second modem. For example, the particular timing recovery and automatic gain control schemes used by the receiver portion of the second modem may be optimally initialized with a synchronization signal having a specific length, amplitude, or spectrum. In one embodiment, a synchronization signal is configured to convey a single frequency tone for use during a synchronization routine. The modem system may also employ similar techniques to generate, transmit, and analyze a programmable line impairment learning signal.

Abstract: An improved echo canceler training technique may be employed by a digital server modem in a PCM modem context, such as a V.90 modem system. The disclosed echo canceler training technique establishes the digital impairments within the echo path by transmitting a training signal from a transmitter located at the digital server modem. The echo signal generated in response to the training signal is received by the digital server modem and appropriately analyzed to accurately model the echo path. The echo canceler resident at the server modem is than suitably trained to compensate for the modeled echo path. In the preferred embodiment, the echo canceler training signal is also used during in the context of downstream digital impairment learning by the analog client modem. In the context of the echo canceler training, the server modem does not rely upon any processing or analysis performed by the client modem; the server modem trains its echo canceler without receiving any information from the client modem.

Abstract: A modem system includes a programmable synchronization signal format that can be configured at a first modem in response to a request received from a second modem. The synchronization signal format may define a number of parameters of the synchronization signal, such as the sign pattern for symbols transmitted by the first modem during a training sequence. The specific parameters of the synchronization signal format may be associated with the design and operation of the second modem. For example, the particular timing recovery and automatic gain control schemes used by the receiver portion of the second modem may be optimally initialized with a synchronization signal having a specific length, amplitude, or spectrum. In one embodiment, a synchronization signal is configured to convey a single frequency tone for use during a synchronization routine. The modem system may also employ similar techniques to generate, transmit, and analyze a programmable line impairment learning signal.

Abstract: A method and apparatus for controlling and shaping the spectrum of transmitted signal samples having predetermined frequency characteristics and allowable transmit signal levels. A running measure of unwanted components is measured and, for each block of the transmitted samples, an objective function based on the previously calculated running measure is computed. Depending upon the measurements, redundancy is determined and selected for each block of the transmitted samples. Accordingly, at least one redundant sample may be added or, the sign of the sample modified, at structured or randomized locations within the block to optimize the objective function.

Abstract: To compensate for the substantially non-uniform spacing of constellation points in a pulse code modulation modem, the transmitting power efficiency is substantially maximized while substantially limiting the complexity of the mapping. To optimize the transmitting power efficiency, the present invention suitably determines an approximate cost function g(n) to reduce the complexity and the 2K lowest cost N-tuples (m0,m1, . . . ,mN-1) for power transmission efficiency. Knowing the lowest cost N-tuples, fractional K data bits are systematically mapped uniformly onto the 2K lowest cost N-tuples.

Abstract: A pulse code modulation modem system utilizes the same total average transmit power formula for designing signal point constellations and for verifying that the transmit power of the signal point constellations are within a designated maximum power limit. The transmit power of the signal point constellations designed by the client modem is also calculated by the server modem to verify that the transmit power limit imposed upon the server modem is not exceeded. In addition, the modem system is capable of designating a transmit power limit associated with one or more training signal points or a training sequence for use during a training mode.

Abstract: An improved apparatus for implementing shell mapping in a PCM modem incorporates u-law signal mapping points. An improved signal point encoding technique effectively employs ring-indices that are generated in accordance with known principles. The ring indices are applied to a reordering module, which rearranges the ring indices produced by a conventional shell mapping algorithm. A preferred reordering scheme takes advantage of the non-uniform probability distribution provided by the conventional shell-mapping algorithm. The rings are rearranged such that the sets of signal points having relatively small separation distances are assigned to rings with relatively low frequencies of occurrence, while the sets of signal points having relatively large separation distances are assigned to rings with relatively high frequencies of occurrence. The reordering scheme optimizes the signal point assignment while maintaining acceptable limits for average transmission power.

Abstract: A modem system includes a programmable synchronization signal format that can be configured at a first modem in response to a request received from a second modem. The synchronization signal format may define a number of parameters of the synchronization signal, such as the sign pattern for symbols transmitted by the first modem during a training sequence. The specific parameters of the synchronization signal format may be associated with the design and operation of the second modem. For example, the particular timing recovery and automatic gain control schemes used by the receiver portion of the second modem may be optimally initialized with a synchronization signal having a specific length, amplitude, or spectrum.

Abstract: A method and apparatus for performing spectral shaping transmitted samples with a set of predetermined frequency characteristics and a predetermined set of allowable transmitted signal levels are disclosed. The method first calculates, for each of the transmitted samples, a running measure of unwanted components upto the current sample. It then computes, for each block of the transmitted samples, an objective function based on the running measure previously calculated. It then selects, for each block of the transmitted samples, at least one redundant sample to be added or at least one transmitted sample to be modified, at structured or randomized location within the block to optimize the objective function. The location of the dependent sample can further be fixed, scrambled (pseudo random) or randomized. The method of computing can be any one of the following: a Running Filter Sum, a Running Fourier Transform (“RFT”) or Fast FT (“RFFT”), or an RDS, for each transmitted sample.

Abstract: A pulse code modulation modem system utilizes the same total average transmit power formula for designing signal point constellations and for verifying that the transmit power of the signal point constellations are within a designated maximum power limit. The transmit power of the signal point constellations designed by the client modem is also calculated by the server modem to verify that the transmit power limit imposed upon the server modem is not exceeded. In addition, the modem system is capable of designating a transmit power limit associated with one or more training signal points or a training sequence for use during a training mode.

Abstract: An improved apparatus for implementing shell mapping in a PCM modem incorporates .mu.-law signal mapping points. An improved signal point encoding technique effectively employs ring indices that are generated in accordance with known principles. The ring indices are applied to a reordering module, which rearranges the ring indices produced by a conventional shell mapping algorithm. A preferred reordering scheme takes advantage of the non-uniform probability distribution provided by the conventional shell mapping algorithm. The rings are rearranged such that the sets of signal points having relatively small separation distances are assigned to rings with relatively low frequencies of occurrence, while the sets of signal points having relatively large separation distances are assigned to rings with relatively high frequencies of occurrence. The reordering scheme optimizes the signal point assignment while maintaining acceptable limits for average transmission power.

Abstract: A pulse code modulation modem system is configured to transmit data from a first modem to a second modem over the public switched telephone network (PSTN). The PSTN employs robbed bit signaling (RBS) such that symbols affected by RBS arrive at the second modem in a periodic manner based on a period of six symbols. The modem system is configured such that signal segments are formatted and transmitted with six symbols per segment. After obtaining symbol synchronization, the second modem initializes a modulo-6 symbol counter such that the zero count corresponds to the first symbol of each received signal segment. Those symbols affected by RBS are identified and analyzed to determine optimized signal point constellations that may be used to compensate for the RBS on a symbol-by-symbol basis during subsequent encoding and decoding. Upon a loss of synchronization, the second modem resets its modulo-6 counter in response to the detection of the first symbol in a subsequent signal segment.

Abstract: A method is disclosed for encoding and modulating bits of an information stream and transmitting them over a designated channel in a high speed communication system. The method includes the steps of dividing a set of the entire constellation of available points into a finite plurality of zero parity vectors defined by two criteria, namely that (1) the column vectors have odd parity and (2) a group of a predefined integer number of column vectors have a 0 modulus (i.e. be divisible by a given number). Column vectors forming only a partially dimensioned portion of the code (e.g. 4D) corresponding to one discrete baud interval are preferably transmitted in a systematic form and with sufficient coding gain for adaptive DFE equalization and whereby a group of column vectors corresponding to an integer number of successive baud intervals that form the fully dimensioned code (e.g.