Abstract: A coherent RAKE receiver utilizes a "blind block" path gain estimation scheme, based on a maximum likelihood criterion, to estimate path gains in the receiver. It is "blind" in that preliminary hard decisions on coded bits (i.e., coded bits from the corrupt transmitted signal) are not used. Instead, a form of soft decisions are used. It is a "block" scheme in that the complex path gains are estimated for an isolated block, for example a block of B correlator outputs. The path gains varying with time are approximated to be linear in time such that the average path gain and the slope of the path gain per path can be utilized to estimate the path gain. The path gain estimation scheme overcomes the shortcomings of typical CDMA systems where there is no assurance of continuous transmission (except for full-rate 9600 b/s transmission) upon which to base a FIR filter-type prediction scheme.

Abstract: A method and apparatus is provided for transmitting spread spectrum signals. The transmitter receives data symbols. Subsequently, the transmitter splits each particular set of two received data symbols into a first and second array of data symbols according to either of two algorithms. The first algorithm including providing both data symbols of the particular set to the first and second array of data symbols and the second algorithm including providing one of the data symbols of the particular set to the first array of data symbols and the other of the data symbols of the particular set to the second array of data symbols. Subsequently, the transmitter determines particular channels to transmit the first and second array of data symbols by spreading the first and second array of data symbols with a predetermined length Walsh code.

Abstract: A method and apparatus is provided for transmitting spread spectrum signals. The transmitter receives data bits at a particular rate. Subsequently, the transmitter encodes the received data bits at a predetermined encoding rate into data symbols. Subsequently, the transmitter derives predetermined length orthogonal codes from the data symbols. The transmitter accommodates variable received data bit rates by setting the predetermined encoding rate and the predetermined orthogonal code length in response to the received data bit rate. Subsequently, the transmitter spreads the derived orthogonal codes with a user PN spreading code.An alternative method and apparatus is provided for transmitting spread spectrum signals. The transmitter receives data bits at a particular rate. Subsequently, the transmitter encodes the received data bits at a predetermined encoding rate into data symbols.

Abstract: A method and apparatus is provided for encoding and decoding. In encoding, bits (202) are encoded (204) into symbols (206) such that maximum likelihood decoding is facilitated. Groups of symbols (206) are translated by either interleaving by group each group within a block (208) and subsequently deriving an orthogonal code from each group (212) or deriving an orthogonal code from each group and subsequently interleaving by code each code within a block. In decoding, groups of samples (228, 229) are transformed by either generating metrics and index symbols (242) for each group of samples (232, 234, 236, 238, 240) and subsequently deinterleaving by group each group of metrics within a block (244) or deinterleaving by group each group of samples within a block and subsequently generating metrics and index symbols for each deinterleaved group of samples. Each metric represents the confidence that a group of samples is a particular orthogonal code.

Abstract: A method and apparatus is provided for encoding and decoding. In encoding, bits (202) are encoded (204) into symbols (206) such that maximum likelihood decoding is facilitated. Groups of symbols (206) are translated by either interleaving by group each group within a block (208) and subsequently deriving an orthogonal code from each group (212) or deriving an orthogonal code from each group and subsequently interleaving by code each code within a block.In decoding, groups of samples (228, 229) are transformed by either generating metrics and index symbols (242) for each group of samples (232, 234, 236, 238, 240) are subsequently deinterleaving by group each group of metrics within a block (244) or deinterleaving by group each group of samples within a block and subsequently generating metrics and index symbols for each deinterleaved group of samples. Each metric represents the confidence that a group of samples is a particular orthogonal code.

Abstract: A full-duplex, two-wire Nyquist sampled data communication system includes an adaptive echo canceller (24) at each terminal (e.g., 10'). The echo canceller generates a replica (z.sub.m) of the echo component of each sample (r.sub.M) of the incoming signal. The replica and the sample are subtractively combined to provide an echo compensated signal (S.sub.M). During intervals of simultaneous transmission and reception, i.e., double talk, the echo compensated signal may contain not only an uncancelled echo component but also a far-end data component. An adaptation error signal generator (80), operating in response to a stream of recovered data symbols (e.g., a.sub.n), estimates and removes the far-end data component from the echo compensated signal and, in response to the difference, generates an adaptation error signal (.gamma.E.sub.M-D). This signal is applied as an error signal to the echo canceller.

Abstract: Asynchronous digital frequency shift keyed (FSK) signals are demodulated by using an autocorrelation type demodulator including digital integration. To this end, the autocorrelation function and digital integration are realized by generating integration increments, i.e., area increments, at the digital signal sampling points and accumulating them to obtain the integrated output. This is realized by turning to account a relationship between zero crossings of the received signal, zero crossings of a delayed version of the received signal and polarity of the product of the received signal and its delayed version relative to sampling points of the received digital signal. Specifically, the area increment in an n.sup.th sampling interval is determined by the time interval since the last zero crossing of the received signal before the n.sup.th sampling point, the time interval since the last zero crossing of the delayed signal before the n.sup.th sampling point and the polarity of the product signal at the n.sup.

Abstract: A feedforward nonlinear signal (P(n)) is added to each sample of a linearly equalized received signal (Q(n)) to provide compensation for nonlinear intersymbol interference. The received signal is a modulated data signal impaired by linear and nonlinear distortion as well as phase jitter and additive noise. The feedforward nonlinear signal added to each sample is comprised of a weighted sum of products of individual ones of the samples and their complex conjugates. Each multiplicand bears a predetermined temporal relationship to the sample currently being processed. In an illustrative embodiment, compensation for second- and third-order intersymbol interference is provided by including two- and three-multiplicand weighted products in the feedforward nonlinear signal. Weighting coefficients for each product are adaptively updated in a decision-directed manner.

Abstract: A receiver for a quadrature amplitude modulated data signal impaired by linear and nonlinear distortion, phase jitter and additive noise includes circuitry which compensates for these impairments. In particular, the receiver includes a processor (FIG. 1 44; FIG. 2, 44')which subtracts a feedback nonlinear signal (FIG. 1, D(n); FIG. 2, D'(n)) from each sample of the received signal, either prior or subsequent to demodulation, providing compensation for nonlinear intersymbol interference. The feedback nonlinear signal subtracted from each sample is comprised of a weighted sum of products of individual data decisions and/or the complex conjugates of data decisions, each such product, in turn, being multiplied by a predetermined harmonic of the carrier frequency. In an illustrative embodiment, compensation for second- and third-order intersymbol interference is provided by including two- and three-multiplicand weighted products in the feedback nonlinear signal.

Abstract: An adaptive equalizer and echo canceller jointly respond to a common error difference between the actual output and the quantized digital output of a data receiver in a two-wire digital data transmission system to achieve simultaneous full-bandwith full-duplex operation. Two-wire transmission channels are typically terminated in hybrid balancing networks which because of their fixed impedances permit "echoes" of the transmitted signal to interfere with reception of the much weaker incoming signal. Both the equalizer and canceller are adaptively adjustable transversal structures.

Abstract: A receiver for a quadrature amplitude modulated data signal impaired by linear and nonlinear distortion, phase jitter and additive noise includes circuitry which compensates for these impairments. In particular, the receiver includes a processor (FIG. 1 44; FIG. 2, 44') which subtracts a feedback nonlinear signal (FIG. 1, D(n); FIG. 2, D'(n)) from each sample of the received signal, either prior or subsequent to demodulation, providing compensation for nonlinear intersymbol interference. The feedback nonlinear signal subtracted from each sample is comprised of a weighted sum of products of individual data decisions and/or the complex conjugates of data decisions, each such product, in turn, being multiplied by a predetermined harmonic of the carrier frequency. In an illustrative embodiment, compensation for second- and third-order intersymbol interference is provided by including two- and three-multiplicand weighted products in the feedback nonlinear signal.