Abstract: A method of transmitting data in a cable modem system includes the steps of encoding the data using forward error correction. The data is then encoded with Turbo encoding. The data is then sent to a modulation scheme. The data is then transmitted over a cable channel. The data is then demodulated. The data is then decoded using a Turbo decoder. An inverse of the forward error correction is then applied to the data.

Abstract: A receiver includes a filter for filtering a received signal to produce a filtered signal. A converter converts the filtered signal to a baseband signal that is substantially free of an initial frequency offset and inter-symbol interference (ISI), responsive to a frequency-offset estimate and a restorative signal that compensates for the ISI. A detector detects symbols in the baseband signal to produce a decision signal. A restorative signal generator generates, from the decision signal, the restorative signal responsive to the frequency-offset estimate, such that the restorative signal compensates for the ISI.

Abstract: Signal processing under attenuated transmission conditions. Within an orthogonal signal space, the number of orthogonal signals that are used to transmit information from a transmitter to a receiver is reduced and the transmitted power of each of the now remaining orthogonal signals is modified; this may involve increasing the power of all of the remaining orthogonal signals equally or alternatively modifying them individually. The same modulation used before the reduction may also be used afterwards; within communication systems having multiple transmitter-receiver paths, this will ensure that the communication system's throughput and efficiency will remain unchanged even when one (or more) transmitter-receiver paths are highly attenuated. In addition, robust mode operation is provided for ranging and registering of transmitter devices when entering the communication system.

Abstract: A receiver includes a filter for filtering a received signal to produce a filtered signal. A converter converts the filtered signal to a baseband signal that is substantially free of an initial frequency offset and inter-symbol interference (ISI), responsive to a frequency-offset estimate and a restorative signal that compensates for the ISI. A detector detects symbols in the baseband signal to produce a decision signal. A restorative signal generator generates, from the decision signal, the restorative signal responsive to the frequency-offset estimate, such that the restorative signal compensates for the ISI.

Abstract: Successive interference canceling for CMDA. ICI may result from a signal's multipath effects, or by filtering/suppression of some of the component energy of the signaling waveforms. Energy component attenuation destroys orthogonality of CDMA symbols thereby causing ICI. An ICF suppresses frequency domain portions (attenuates ingress), but also introduces ICI. Following the ICF, the signal is de-spread, sliced, re-spread and convolved with the ICF echoes (except first tap echoes). Convolving re-spread hard decisions with delayed ICF taps is equivalent to partially re-modulating the first-pass hard decisions to efficiently “add-back-in” the signal energy which was blanked/subtracted by the ICF. Alternatively, parameter estimation de-rotates and re-rotates soft symbols and hard decisions, respectively, compensating for undesirable symbol rotation. The convolved signal is subtracted from a delayed version of the ICF output signal.

Abstract: Improved frequency drift and phase error compensation in a VOFDM receiver. The invention is operable to compensate for frequency drift and phase error within a window that may include a single frame, a sub-frame, or multiple frames. The compensation is performed after having performed estimation of the phase within the particular window; any phase error and frequency drift may be identified and an appropriate form of compensation may be identified to perform curve fitting of the phase within the compensation window. The curve fitting of the phase is performed using linear techniques in one embodiment; an average phase and appropriate slope/ramp are calculated to match the phase as accurately as possible. Other alternative compensation techniques may also be performed, including higher order curve matching techniques. The receiver is operable to perform any necessary compensation before passing the now-compensated data to a symbol processing functional block.

Abstract: Optimal decision metric approximation in bit-soft decisions. The present invention provides for calculation of the decision metrics/branch metrics for determining whether an incoming analog signal should be transformed into a 1 or a 0 in the digital realm. In performing these decisions, there is some probability associated with the decision to map the incoming signal to a value of 1 or 0. These decisions made in extracting bits from a particular symbol are typically referred to as bit-soft decisions. In making these bit-soft decisions, decoders commonly use decision metrics/branch metrics as mentioned above. Whereas prior art approaches typically are very computationally intensive to calculate these values, the present invention provides for a much improved and simplified calculation of decision metrics/branch metrics that may be used in bit-soft decisions. The optimal metric approximation may be implemented using a few mathematical operations and simple comparison logic circuitry.

Abstract: Characterizing channel response in a single upstream burst using redundant information from training tones (TTs). The invention is operable to utilize inserted TTs, contained within a transmitted data frame, to provide for an improved estimate of a communication channel's actual response and an improved estimate of the noise of the communication channel. The invention determines a maximum allowable delay spread of the many communication paths within a multi-path communication channel. Using the redundant TTs information, then a portion of the finite impulse response of the communication channel, within the time domain, may be zeroed, thereby providing a much improved channel estimate and noise estimate. Using the redundant TTs, less noise is introduced onto the data tones (DTs) within a data frame. The present invention is also able to identify those portions of the TTs that are attributable to the actual channel and those that are attributable to the channel's noise.

Abstract: Cancellation of interference in a communication system with application to S-CDMA. A relatively straight-forward implemented, and computationally efficient approach of selecting a predetermined number of unused codes is used to perform weighted linear combination selectively with each of the input spread signals in a multiple access communication system. If desired, the predetermined number of unused codes is always the same in each implementation. Alternatively, the predetermined number of unused codes are selected from within a reordered code matrix using knowledge that is shared between the two ends of a communication system, such as between the CMs and a CMTS. While the context of an S-CDMA communication system having CMs and a CMTS is used, the solution is generally applicable to any communication system that seeks to cancel narrowband interference. Several embodiments are also described that show the generic applicability of the solution across a wide variety of systems.

Abstract: Modified branch metrics for processing bit-soft decisions to account for phase noise impact on cluster variance (CV). The present invention is able to partition a modulation scheme's constellation into two or more regions, so that the bit-soft decision branch metrics may be adjusted based on the CV of the various constellation points. A confidence level may be attached to the various constellation points based on their particular CVs. There are a number of methods to ascertain the CV of the constellation's points, including finding characteristics of various components in a communication system (transmitter, communication channel and receiver), and any method may be used within various embodiments. The modification of the branch metrics/confidence level may be performed in a communication receiver; the communication receiver may be implemented in a communication system employing the vector orthogonal frequency division multiplexing (VOFDM) portion of the broadband wireless internet forum (BWIF).

Abstract: Vector orthogonal frequency division multiplexing (VOFDM) receiver correlation matrix processing using factorization. Efficient correlation matrix processing is used to combine multiple signals into a single combined signal. This single combined signal may be viewed as being a beam form soft decision. An efficient square root factorization system and method provides for computational resource savings while, at the same time, providing for greater precision of the overall computational results. By reducing intermediate variable calculation dynamic ranges, the overall calculation becomes more precise. Particularly within fixed-point arithmetic applications, a reduction in dynamic range of the intermediate variable calculations provides for a significant increase in final calculation precision.

Abstract: Enhanced DOCSIS upstream channel changes. A CMTS directs channel changing of a CM, sometimes between upstream data bursts. Logical channels, part of a single frequency channel, may be used, and the channel changing may be performed between those logical channels. Multiple upstream burst profiles and/or modulation densities may be used providing high degrees of robustness, fidelity, and throughput and allowing great channel flexibility. A CM may be switched between channels without losing transmitter capability. Even if some throughput rate may be sacrificed during the channel changing, the CM will still be able to continue data throughput. Then, the new channel may then undergo the initialization and ranging processes thereby enabling greater throughput on that new channel. After undergoing the initialization and ranging processes, the new channel will then be a fully equivalent member of the CM communication system.

Abstract: A system, method and computer program product is provided for mitigating the effects of burst noise on packets transmitted in a communications system. A transmitting device applies an outer code, which may include, for example, a block code, an exclusive OR (XOR) code, or a repetition code, to one or more packets prior to adaptation of the packets for transmission over the physical (PHY) layer of the communications system, wherein the PHY layer adaptation may include FEC encoding of individual packets. The outer coded packets are then separately transmitted over a channel of the communications system. A receiving device receives the outer coded packets, performs PHY level demodulation and optional FEC decoding of the packets, and then applies outer code decoding to the outer coded packets in order to restore packets that were erased during transmission due to burst noise or other impairments on the channel.

Abstract: Systems and methods are disclosed for detecting and mitigating temporary high-level impairments, in a communications channel, and subsequently, mitigating the deleterious effects of the dynamic impairments. The system includes a transmitter and a receiver. The transmitter is adapted to transmit at least one set of modulated signals. The receiver is adapted to receive the at least one set of modulated signals and mitigate temporary high-level impairment in the at least one set of modulated signals using at least one error vector received during the temporary high-level impairment.

Abstract: A receiver includes a filter for filtering a received signal to produce a filtered signal. A converter converts the filtered signal to a baseband signal that is substantially free of an initial frequency offset and inter-symbol interference (ISI), responsive to a frequency-offset estimate and a restorative signal that compensates for the ISI. A detector detects symbols in the baseband signal to produce a decision signal. A restorative signal generator generates, from the decision signal, the restorative signal responsive to the frequency-offset estimate, such that the restorative signal compensates for the ISI.

Abstract: The present invention relates a system and method for mitigating impairment in a communication system. In one embodiment, the system comprises a transmitter adapted to transmit at least one signal and a receiver adapted to receive the at least one signal and mitigate inter code interference in the signal using at least one inter code interference coefficient.

Abstract: Systems and methods are disclosed for detecting temporary high level impairments, such as noise or interference, for example, in a communications channel, and subsequently, mitigating the deleterious effects of the dynamic impairments. In one embodiment, a preliminary decision is made on at least one signal transmitted over the communications channel. The at least one signal is remodulated and the impairment is determined using the at least one remodulated signal.

Abstract: Systems and methods are disclosed for to compensating reference frequency drift in a communications system having a plurality of modems and a headend, where the system requires critical upstream timing. One embodiment of the method includes learning or determining the relative delay of each modem and reporting each modem's unique delay (relative to the closest modem) to the headend. The method further includes the headend monitoring its own reference for frequency drift, the modem broadcasting pertinent frequency drift information to the modems and adjusting the modems' upstream timing to account for each modem's unique distance (i.e., delay) combined with the broadcast stream of frequency drift information.

Abstract: A filter settings generation operation includes sampling a communication channel to produce a sampled signal. The sampled signal is spectrally characterized across a frequency band of interest to produce a spectral characterization of the sampled signal. This spectral characterization may not include a signal of interest. The spectral characterization is then modified to produce a modified spectral characterization. Filter settings are then generated based upon the modified spectral characterization. Finally, the communication channel is filtered using the filter settings when the signal of interest is present on the communication channel. In modifying the spectral characterization, pluralities of spectral characteristics of the spectral characterization are independently modified to produce the modified spectral characterization. Modifications to the spectral characterization may be performed in the frequency domain and/or the time domain.

Abstract: A single carrier cable modem can be initialized on multiple channels. By initializing a cable modem on more than one channel, the error rate performance of short data packets in cable modems in an impulsive noise environment is improved. The advantage of low symbol rate transmission for short packets in an impulse noise environment is achieved without sacrificing burst capacity at a cable modem and without the complexity of transmitting multiple symbol waveforms simultaneously at a cable modem.