Abstract: Modems, methods, and computer program products identify a signaling alphabet that is in variance with an ideal alphabet due to digital impairments and is used to decode received data symbols. In particular, a set of alphabet thresholds are established that correspond to the data symbols. The data symbols are received in an equalizer, which generates output symbols in response thereto. A collection of data symbols corresponding to a particular alphabet threshold are accumulated and an average value is computed, which is then used to replace the current value for the particular alphabet threshold to which the average value corresponds. Equalizer performance is enhanced as the improved accuracy of the alphabet thresholds results in better error information being fed back for adapting the equalizer filter coefficients.

Abstract: A Viterbi decoder which conducts maximum likelihood decoding of a convolutional code based on Viterbi algorithms including a branch metric generation circuit for generating a branch metric based on input data, an ACS execution circuit for conducting ACS processing using a generated branch metric, a path memory for storing a path selected by ACS processing, a path metric holding circuit for storing new path metric data generated by ACS processing and returning the data again to the ACS execution circuit, and an address generation circuit for conducting generation of a memory address and memory switching control in the path metric holding circuit, and a number of states counter for instructing the branch metric generation circuit and the address generation circuit on a processing cycle, the branch metric generation circuit executing the branch metric generation processing in multiplexing and the ACS execution circuit executing the ACS processing in a multiplicity corresponding to the branch metric generation pr

Abstract: A noise canceling method and apparatus for canceling noise by time domain processing sub-bands of a digital input signal. The input signal is divided into a number of frequency-limited time-domain sub-bands. Each sub-band is then individually processed to cancel noise present in the signal. The noise processing includes exponential averaging of the input, noise estimation, and subtraction processing. The noise subtraction process is simplified by generating a filter coefficient that is exponentially smoothed, hard limited, and multiplied with the input signal to generate the noise processed output for each sub-band. The noise processed bands are then recombined into a digital output signal. Implementation may be effected in software or hardware and applied to various noise canceling and signal processing applications.

Abstract: An apparatus and method are provided for generating a plurality of data frames in a DSL modem configured as an HTU-C device using a single clock source. The technique of the present invention generates a data clock signal by combining a first clock signal provided by a clock source and a receiver overhead signal provided by framing circuitry for indicating the insertion of frame overhead bits into a data frame. The generated data clock signal has the characteristics such that, while the receiver overhead signal is inactive, the data clock signal is active at a frequency substantially equal to frequency of the first clock signal, and while the receiver overhead signal is active, the data clock signal is inactive. The result of this technique is that incoming data is clocked into the data frame at a data rate substantially equal to the frequency of the first clock signal only during time intervals when frame overhead bits are not being inserted into the one data frame.

Abstract: A method for mitigating multipath effects in radio systems which is based on searching for and finding a maximum likelihood estimate of range for a received signal is provided. In determining the maximum likelihood estimate, the correlation process uses a high resolution step method in processing the received signal sample values to develop an estimation statistic. The estimation statistic using the correlations of the received signal is based on a new derived representative set of coefficients formed from a nonlinear combination of parameters of the received signal transformed into a linearly solvable invertible parameter set allowing solution of the maximization process of the estimation statistic over a reduced dimension search space. Additionally there is a method of constraining the relative amplitude of received secondary signals to obtain a refinement of the optimal solution of range.

Abstract: A CDMA reverse link has a system for providing compensation for phase errors caused by clock jitter in a CDMA reverse link. After filtering, data spread by a pilot PN sequence is supplied to a shift register that produces several data samples for sequential cycles of an internal clock. A memory stores compensation factors representing the clock jitter, pre-calculated for each of the internal clock cycles. A counter counts the internal clock cycles to provide the memory with an address signal indicating a memory location that stores the compensation factor for a current internal clock cycle. Based on the data samples and the compensation factor, an interpolator performs an interpolation algorithm to determine an adjusted spread data value that compensates for phase errors caused by jitter in the internal clock.

Abstract: A GLONASS receiver and a corresponding method for its calibration for more precise carrier phase measurements. The receiver includes a conventional receiver channel (36), having a bandpass filter (40) for establishing the sampling bandwidth prior to digitizing a plurality of received satellite signals, each having a different frequency. The receiver also includes a calibration channel (50) in which multiple satellite signals are bandbass filtered (in filter 58) at a single intermediate frequency, to avoid errors resulting from group delay variation introduced by passing multiple satellite signals through a common bandpass filter. The calibration channel (50) downconverts (56) to the intermediate frequency, bandpass filters (58), and then upconverts (60) again. Each satellite signal in turn is processed in this manner by selecting appropriate difference frequencies for downconversion and upconversion.

Abstract: A method of maximizing a communication parameter, such as data capacity, signal quality or throughput of a channel between a transmit unit with M transmit antennas and a receive unit with N receive antennas and a communication system such as a wireless network (including networks with multiple access techniques such as TDMA, FDMA, CDMA, OFDMA) employing the method. The data is first processed to produce parallel spatial-multiplexed streams SMi, where i=1 . . . k, which are converted or mapped to transmit signals TSp, where p=1 . . . M, assigned for transmission from the M transmit antennas. Corresponding receive signals RSj, where j=1 . . . N, are received by the N receive antennas of the receiver and used to assess a quality parameter, such as a statistical signal parameter including SINR, SNR, power level, level crossing rate, level crossing duration of the signal of a predetermined threshold and reception threshold, or a parameter of the data, such as BER or packet error rate.

Abstract: A decoder also includes a channel estimator to estimate coefficients describing a channel through which the signal has propagated, a signal predictor that combines the channel estimates with corresponding samples of the signal to obtain a metric, and a metric accumulator to accumulate the metrics for hypothesized symbol sequences to determine the likelihood indications. The hypothesized symbol sequences include partial symbols that select a subgroup of the symbol alphabet. This allows those parts of a symbol that are most important for predicting signal samples to be retained in a hypothesized state while the remaining parts can pass to a path history memory, thereby reducing the number of possible states that must be considered.

Abstract: A digital modem for operating in a splitterless environment that supports fast retrain based on communication profiles. The modem includes a memory that stores a plurality of communication profiles, ADSL communication logic that sends and receives information via a phone line and that operates according to any one of the plurality of communication profiles, and signal quality monitor logic that continuously monitors communication on the phone line. The monitor logic provides a signal change indication if the signal quality changes by at least a predetermined amount. The modem further includes fast retrain logic that selects another one of the profiles stored in the memory in response to the signal change indication, that retrains the communication logic to operate according to the selected profile and that cooperates with the communication logic to transmit a fast retrain indication via the phone line to the central office ADSL modem.

Abstract: A circuit for detecting a signal is designed with a first serial circuit coupled to receive an input signal in response to a clock signal. The first serial circuit (121) has N taps (142-146) arranged to produce a respective plurality of first tap signals from the input signal (111). A first logic circuit (130, 132, 134, 148) is coupled to receive the plurality of first tap signals and one of N predetermined signals and the complement of N predetermined signals. The first logic circuit produces a first output signal (150) in response to the clock signal, the plurality of first tap signals and the one of N predetermined signals and the complement of N predetermined signals. A second serial circuit coupled to receive the first output signal. The second serial circuit has M taps (150, 172-184) arranged to produce a respective plurality of second tap signals from the first output signal, wherein a ratio of N/M is no greater than four.

Abstract: A radio receiver converts an original frequency of a modulated received signal into a plurality of digitization frequencies and digitizes the modulated received signal at each one of the plurality of digitization frequencies. The receiver determines a plurality of reception quality measures associated with each one of the digitized modulated received signals at each one of the plurality of digitization frequencies. The receiver demodulates the modulated received signal using a digitized modulated signal at a digitization frequency that provides a better reception quality than those of another digitization frequency.

Abstract: In a wireless data network, such as a General Packet Radio Service (GPRS) network, a transmitter uses one of k coding/modulation schemes for transmitting data. The transmitter initially selects a coding/modulation scheme, C, as a function of carrier-to-interference ratio (C/I) measurements. The transmitter then calculates the number of blocks, B, required to transmit a number of data packets, D, using the coding/modulation scheme C. In addition, the transmitter calculates the number of blocks required to transmit the number of data packets, D, for each coding/modulation scheme that is stronger than the selected coding/modulation scheme C. The transmitter finally selects that coding/modulation scheme that results in transmitting the number of data packets D in B blocks using the strongest coding/modulation scheme. As a result, each block is transmitted using the strongest coding/modulation scheme available.

Abstract: A method and apparatus provide channel estimation for multicarrier systems. A minimum mean-square-error (MMSE) channel estimator makes full use of time-and frequency-domain correlations of the frequency response of time-varying dispersive fading channels. A robust channel estimator that is insensitive to the channel statistics is provided. The robust channel estimator can significantly improve the performance of a multicarrier system such as an orthogonal frequency division multiplexing (OFDM) modulation system in a rapid dispersive fading channel. In addition, the estimation process can employ a new reference generator which can select the source of the reference signal as being a decoded or undecoded signal depending on the correction success rate of the decoder.

Abstract: A DC offset correction loop (200, 300) utilizes a peak estimator (218, 322) to determine peaks associated with a digital signal (238, 338). The peak estimator (218, 322) averages the peaks in order to estimate the DC offset. A summer (216, 326) sums the DC offset (242, 350) with the digital signal to produce a corrected output.

Abstract: The present invention is a novel and improved method and apparatus for performing position location in wireless communications system. One embodiment of the invention comprises a method for performing position location comprising the steps of receiving signal samples, generating a coarse acquisition sequence, rotating the coarse acquisition sequence yielding a rotated coarse acquisition sequence, and applying the rotated coarse acquisition sequence to the signal samples at a set of time offsets yielding correlated output data.

Abstract: Differential transmission of each of two bits D0 and D1 is accomplished with three lines disposed between a transmitting unit and a receiving unit. One of the three lines is a first data line corresponding to the bit D0. Another of the three lines is a second data line corresponding to the bit D1. The remaining one of the three lines is a reference line. When the bits D0 and D1 have different values, without involving the use of the reference line, the second data line serves as a transmission path complementary to the first data line, while the first data line serves as a transmission path complementary to the second data line. When the bits D0 and D1 have equal values, a voltage representing a value obtained by inverting each of the data bits D1 and D1 is supplied to the reference line such that the reference line serves as a transmission path complementary to each of the first and second data lines.

Abstract: A circuit for predistorting a signal to be transmitted via a non-linear channel comprises an envelope detector for detecting an envelope of the signal. A quantization for forming quantized envelope values on the basis of the detected envelope is connected to the envelope detector as well as to a table for supplying complex predistortion coefficients which depend on the quantized envelope values and on a previously detected transmission function of the non-linear channel. An evaluation circuit separated from the non-linear channel and used for the complex evaluation of the signal to be transmitted via the non-linear channel with the complex predistortion coefficients permits the distortion introduced by the non-linear channel to be substantially compensated according to amount and phase.

Abstract: An orthogonal frequency division multiplex (OFDM) modulator of such a system as to add guard intervals to a temporal waveform generated by modulating an input data train into a large number of (sub)carriers, conducting quadrature modulation, and outputting an OFDM signal.

Abstract: The present invention relates to methods and arrangements pertaining to mobile telephone modems. According to the invention, the mobile telephone modem includes memory means in which one or more ranking orders of data bearer services is/are stored. In response to a call request, one of the stored ranking orders is selected. If only one ranking order is stored, this ranking order will, of course, be selected. Calling is first carried out with the highest ranked data bearer service in the selected ranking order. If a call connection is not made, it is determined on the basis of an error message from the mobile telephone network whether or not the highest ranked data bearer service is supported by the mobile telephone network.