Abstract: An apparatus for providing data dependent detection in a data read channel is disclosed. Parameters in a read channel are dynamically adjusted according to data dependent noise. For example, a comparison in an add-compare-select (ACS) unit of a Viterbi decoder may be adjusted or offset terms in error event filters may be biased to choose a Viterbi sequence with more transitions or to compensate for polarity dependent noise.

Abstract: An apparatus that uses a lengthened equalization target filter with a matched filter metric in a Viterbi detector is disclosed. The equalization target includes a base partial response component, i.e., (1?D2), a fractional coefficient polynomial component to whiten the noise, i.e., (1+p1D+p2D2), and a time-reversed replica of the noise-whitening component. Thus, the time-reversed replica of the noise-whitening component comes from what was formerly a matched filter component.

Abstract: Apparatus for detecting data in a sensor signal generated by a read sensor in a local probe data storage device comprises a differentiation for subtracting a value of the sensor signal from the succeeding value of the sensor signal to generate a ternary difference signal; and a convertor connected to the differentiator for converting the difference signal into a binary output signal indicative of the detected data. A local probe data storage device comprising such apparatus is also described.

Abstract: Digital impairments, including Robbed Bit Signaling (RBS) and impairments due to digital attenuation PAD (Packet Assembler/Disassembler) devices, may be identified in sets of Pulse Code Modulation (PCM) signal levels, such as sets of Digital Impairment Learning (DIL) signals transmitted from a server modem to a client modem during a plurality of DIL levels. Both signature analysis and signal level comparison analysis are preformed on the signals to identify digital impairments. Signature analysis compresses the set of signal levels into a signature. Digital impairments are determined based on the signature. In a preferred embodiment, the PCM signal levels are compressed into a signature by identifying clusters and/or skips. PCM signal level comparison analysis uses differences, between PCM signals and models of signals having various digital impairments. By using both techniques combination, the strengths of each technique are utilized while the weaknesses of each techniques are avoided.

Abstract: Methods, systems and computer program products are provided for monitoring performance of a modem which obtain diagnostic data directly from memory associated with the modem's digital signal processor (DSP). A secondary path to the DSP memory is utilized for the monitoring operations so that real time data can be obtained during connection startup procedures and during an active connection. First-in first-out (FIFO) buffers are incorporated in the DSP memory to track state transitions of one or more of the state machines within the modem and various performance data measurements may be obtained directly from the DSP memory responsive to different state transition events. The real time collected data may be stored in a file and provided to a remote location for use in diagnosing customer problems with specific customer line connections. Accordingly, real time monitoring of digital and analog line conditions and modem performance may be utilized to diagnose problems with modems and line connections.

Abstract: Digital impairments in a set of Pulse Code Modulation (PCM) signal levels that are received at a client modem from a server modem are identified by compressing the set of PCM signal levels into a signature. Digital impairments are determined based on the signature. In a preferred embodiment, the PCM signal levels are compressed into a signature by identifying clusters and/or skips in the set of PCM signal levels. In particular, when transmitting PCM signal levels from a server modem to a client modem over a connection that is subject to digital impairments such as Robbed Bit Signaling (RBS) and/or PAD digital impairments and quantization, some adjacent PCM signal levels may become identical or very close to one another. Moreover, other adjacent signal levels may have a difference that is at least approximately twice the difference of other levels. The former phenomenon is referred to as a “cluster” and the latter phenomenon is referred to as a “skip”.

Abstract: Described is a modulation encoder having a finite state machine for converting input bits into output bits in which the number of alternating output bits is limited to j+1 where j is a predefined maximum number of transitions in the output bits, and in which the number of like output bits is limited to k+1 where k is a predefined maximum number of non-transitions in the output bits. The modulation encoder may be employed in encoding apparatus for converting an input bit stream into an output bit stream. Such apparatus may comprise partitioning logic for partitioning the input bit stream into a first group of bits and a second group of bits. A plurality of the aforementioned modulation encoders may be connected to the partitioning logic for converting the first group of bits into coded output bits. Combining logic may be connected to the or each modulation encoder and the partitioning logic for combining the coded output bits and the second group of bits to generate the output bit stream.

Abstract: Modems, methods, and computer program products provide a dual power mode capability in which a maximum power limit is determined for a received signal and, based on that determination, at least one modem operational parameter is adjusted and/or digital impairment learning (DIL) sequence is selected. Adjustments made to the operational parameters may allow a modem to operate in a high power mode to achieve a higher downstream data rate. The higher downstream data rate may be attributed to an improved SNR resulting from an increase in data transmission power. Moreover, the modem may also operate in a normal power mode where the operational parameters may be set to maximize the client modem receiver's dynamic range. By selecting the DIL sequence based on the power limit, a DIL signal containing symbols having power levels within the power limit may be selected.

Abstract: Methods, modems and computer program products for detecting whether a remote modem is of a particular design type and for adjusting the communication configuration for a communication session based on a type of the remote modem. The modem type is recognized based on a knowledge that the modem design of certain manufacturers has a unique associated data pattern contained within the startup communication sequence which is not specified by the protocol but which can be demodulated and detected to thereby recognize that the remote modem is a particular manufacturer's design type. Based on knowledge of the characteristics of the remote modem design, various steps are taken which may improve performance of the communication connection in light of the particular modem design's characteristics. For example, a different Total Harmonic Distortion (THD) threshold may be used for falling back to V.34 communications when the remote modem design only supports up to 2 look ahead for spectrum shaping.

Abstract: Receivers, methods, and computer program products can be used to demodulate a data signal transmitted from a digital source, which has a network sampling rate that is synchronized with a network clock. In an illustrative embodiment, a receiver includes a two-stage interpolator that receives digital samples of the data signal as an input and produces an interpolated digital sample stream to be filtered by an adaptive fractionally spaced decision feedback equalizer. The digital samples received in the interpolator are synchronized with a local clock; however, the interpolated sample stream is synchronized with the network clock. A slicer generates symbols for the samples output from the decision feedback equalizer by comparing the samples with a reference signaling alphabet. The receiver can be used in a V.90 client modem to demodulate pulse code modulated (PCM) data transmitted as pulse amplitude modulated (PAM) signals from a digital network.

Abstract: Modems, methods, and computer program products select a data rate based on error signals in a modem. In an illustrative embodiment, error signals representing the difference between an output of an equalizer and an output of a detector are accumulated and an average error value is computed therefrom. A signal to noise ratio is determined using the average error value. The signal to noise ratio is then used to select a data rate. In another illustrative embodiment, the mean squared error at the output of the equalizer is determined and then used, along with the probability of error in correctly detecting a symbol, to select a data rate. Incorrect decisions in detecting received data symbols can cause a catastrophic failure in a decision feedback equalizer used in a modem receiver as errors are repeatedly fed back causing the tap coefficients for the equalizer filters to be shifted from their normal operating values.

Abstract: Described is a modulation encoder having a finite state machine for converting input bits into output bits in which the number of alternating output bits is limited to j+1 where j is a predefined maximum number of transitions in the output bits, and in which the number of like output bits is limited to k+1 where k is a predefined maximum number of non-transitions in the output bits. The modulation encoder may be employed in encoding apparatus for converting an input bit stream into an output bit stream. Such apparatus may comprise partitioning logic for partitioning the input bit stream into a first group of bits and a second group of bits. A plurality of the aforementioned modulation encoders may be connected to the partitioning logic for converting the first group of bits into coded output bits. Combining logic may be connected to the or each modulation encoder and the partitioning logic for combining the coded output bits and the second group of bits to generate the output bit stream.

Abstract: Modems, methods, and computer program products select a data rate based on error signals in a modem. In an illustrative embodiment, error signals representing the difference between an output of an equalizer and an output of a detector are accumulated and an average error value is computed therefrom. A signal to noise ratio is determined using the average error value. The signal to noise ratio is then used to select a data rate. In another illustrative embodiment, the mean squared error at the output of the equalizer is determined and then used, along with the probability of error in correctly detecting a symbol, to select a data rate. Incorrect decisions in detecting received data symbols can cause a catastrophic failure in a decision feedback equalizer used in a modem receiver as errors are repeatedly fed back causing the tap coefficients for the equalizer filters to be shifted from their normal operating values.

Abstract: Methods, systems and computer program products are provided for constellation generation which determine initial ucode boundaries and an initial minimum signal level spacing. A work constellation set is generated based on the initial ucode boundaries and the initial minimum signal level spacing. The work constellation set is then iteratively adjusted so as to provide an adjusted work constellation set which achieves an error probability target. The adjusted work constellation set is then iteratively pruned so as to provide a pruned work constellation set which achieves a power limit. The pruned work constellation set is then iteratively fine-tuned so as to provide a final constellation set which is within a specified tolerance of the error probability target and/or the power limit.

Abstract: Error rate control systems, methods, and computer program products request a data rate slow-down based on the status of the error rate. A linear penalty is generated if a data rate slow-down is requested, which is then used to determine a minimum distance between constellation points in a signaling constellation or alphabet. Because the minimum distance between constellation points may be directly related to the error probability, the error rate may be controlled through the linear penalty.

Abstract: Robbed Bit Signaling (RBS) and PAD digital impairments in sets of Digital Impairment Learning (DIL) signals that are repeatedly transmitted from a server modem to a client modem during DIL intervals are identified by identifying a PAD level for the sets of DIL signals in the DIL intervals and then identifying an RBS type for individual sets of DIL signals based upon the PAD levels so identified. The PAD level may be identified using model DIL signals that correspond to PAD levels that are not subject to RBS. The RBS type may be identified using model DIL signals that correspond to multiple RBS types that are subject to the identified PAD level. More specifically, one of the DIL intervals that contains DIL signals that are not subject to RBS is identified. A PAD level for the DIL signals in the one of the DIL intervals so identified then is determined.

Abstract: Modems, methods, and computer program products select a data rate based on error signals in a modem. In an illustrative embodiment, error signals representing the difference between an output of an equalizer and an output of a detector are accumulated and an average error value is computed therefrom. A signal to noise ratio is determined using the average error value. The signal to noise ratio is then used to select a data rate. In another illustrative embodiment, the mean squared error at the output of the equalizer is determined and then used, along with the probability of error in correctly detecting a symbol, to select a data rate. Incorrect decisions in detecting received data symbols can cause a catastrophic failure in a decision feedback equalizer used in a modem receiver as errors are repeatedly fed back causing the tap coefficients for the equalizer filters to be shifted from their normal operating values.

Abstract: Methods, systems and computer program products are provided for refining constellation values in a Pulse Code Modulated (PCM) code point sequence of a PCM modem by averaging received levels associated with received symbols for a code point of interest received during data mode operation of the PCM modem so as to provide an average received level for the code point of interest and revising a constellation value corresponding to the code point of interest in the PCM code sequence based on the average received level for the code point of interest so as to provide a refined constellation value. Preferably, the averaging is performed by detecting that a symbol corresponding to the code point of interest has been received by the PCM modem and incorporating the received level of the symbol into a running sum of previously received levels for the symbol. If a predefined number of received levels have been incorporated into the running sum then the running sum is divided by the predefined number of receive levels.

Abstract: A method for decoding Low Density Parity Check (LDPC) codes comprises executing a sum product algorithm to recover a set of information bits from an LDPC code represented as a bipartite graph of symbol nodes and check nodes, the sum product algorithm being responsive to input log likelihood ratios associated with the symbol nodes.

Abstract: A method and apparatus are provided for implementing soft-input soft-output iterative detectors/decoders. Soft-input information is added directly to incoming channel samples. Input signals comprising the received incoming channel samples with the added soft-input information are detected using a detector trellis. Branch metric terms are transformed to shift all time varying terms with the added soft-input information and some constant terms after an add compare select (ACS) unit. The shifted time varying terms with the added soft-input information and the shifted constant terms are added directly to state metric terms. The soft-input information is added directly to incoming channel samples and the computation of branch metrics is not affected. This allows optimization of a dual-max detector and soft-input soft-output Viterbi detector architectures to minimize hardware complexity and power consumption.