Abstract: A method for modulating a sequence of data symbols such that the transmit signal exhibits spectral redundancy. Null symbols are inserted in the sequence of data symbols such that a specified pattern of K data symbols and N-K null symbols is formed in every period of N symbols in the modulated sequence, N and K being positive integers and K being smaller than N.

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: 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: A wireless device and system employs a two-dimensional (2-D) Trellis code that can be applied to Quadrature Phase Shift Keying (QPSK) and higher order Quadrature Amplitude Modulation (QAM) constellations. The Trellis codes employed have optimal Euclidean distance properties for QPSK constellations, and have very good Euclidean distance properties for higher-order QAM constellations. The Trellis codes are suited for transmission systems that adopt multi-mode QPSK and QAM constellations with different data rates since the same Trellis code can be applied to all modulation formats and the same decoder can be used at the receiver for all modulation formats. Modulation formats include QPSK, 8-QAM, 16-QAM, 32-QAM, and 64-QAM and may be extended to even higher order modulations formats.

Abstract: In a communication system, Huffman coding techniques are used to obtain shaping gains for an improvement in data transmission rates. More particularly, a novel method of Huffman shaping is described that achieves a shaping gain of greater than 1 dB. The shaping gain results in a higher data rate transmission in a communication system where transmitted power is constrained.

Abstract: Various systems and methods related to equalization precoding in a communications channel are disclosed. In one implementation preceding is performed on signals transmitted over an optical channel. In one implementation preceding and decoding operations are performed in parallel to facilitate high speed processing in relatively low cost circuits. Initialization of the precoders may be realized by transmitting information related to the characteristics of the channel between transceiver pairs.

Abstract: Trellis-enhanced precoding for trellis-coded transmission over channels with intersymbol interference allows coding and shaping gains to be achieved with minimal transmit power penalty for arbitrary signal constellations, provided the intersymbol interference channels are linearly invertible. This technique can be employed for trellis-coded transmission over a variety of communication channels. However, if the channel response exhibits spectral nulls, trellis-enhanced precoding cannot be applied because the corresponding inverse precoding operation at the receiver requires inverse channel filtering. For channels with a spectral null, this inverse operation can result in unlimited error propagation. The present invention allows trellis-coded transmission over channels exhibiting spectral nulls without incurring unlimited error propagation in the receiver. Coding gains are achieved with minimal transmit power penalty, like in the case of trellis-enhanced preceding.

Abstract: Adaptive analog equalizer permitting 16 Mbit/s token ring (TR) transmission over unshielded twisted-pair (UTP) cables. The equalizer (29) is located at the wiring concentrator (25), and consists of a variable and a fixed filter section. The existing TR receiver (49) and transmitter (53) remain unchanged. To compensate for distortion introduced by the cable section (19b) preceding the equalizer, the level of the signal (B) at the equalizer output (35) is used as a control criterion. The additional distortion contributed by the cable section (21a) following the equalizer is accounted for by measuring the level of the signal (D) received from the transmitter (53) of the next TR station. By these two measurements, the equalizer is adjusted such that the cable-length dependent distortion is eliminated at the next receiver (49).

Abstract: Multiple operating configurations in data circuit terminating equipment (DCE) are enabled through multiple queues stored in a random access memory and which are loaded with bits and characters coming either from data terminating equipment (DTE) or the telecommunications line. The DSP processor stores bits provided by a transmit circuit in a first queue, determines characters from the bits stored in the first queue based on a first transmission protocol and stores the characters in a second queue. A third queue is used by a control processor to store characters to be transmitted to a remote DCE. The DSP processor determines bits to be transmitted from the characters stored in a third queue based on a second transmission protocol, and stores those bits in a fourth queue. When the DCE is operating in a synchronous mode, the DSP processor determines PCM words for transmission based on the contents of the second queue and stores them in a fifth queue for transmission.

Abstract: Data Circuit Terminating Equipment (DCE) allows the connection of a Data Terminal Equipment (DTE) to a telecommunication line. The DCE includes timing elements for providing the DTE with any desired transmitter signal element timing and any desired receiver signal element timing. The timing elements include processing elements for computing a sequence of digital values A(n) and for deriving therefrom a corresponding sequence of interrupt signals T(n). The receiver signal element timing, the transmitter signal element timing, the transmit sampling clock pulsing the D/A converter and the receive sampling clock pulsing the A/D converter are all controlled by different sequences of digital values computed by the processing elements.

Abstract: Method and apparatus for determining occurrence of an S1 modem identification sequence is disclosed. An S1 sequence is found to exist when the sum of conjugate complex multiplication of signal sample amplitudes taken at an interval T/2 result in a negative scalar value for an arbitrary number of sequential occurrences. Complex samples taken from incoming baseband waveform at twice the modulation rate are interleaved in pairs of two with two even numbered samples and two odd numbered samples being considered separately by first performing complex multiplication followed by scalar multiplication of an output of the complex multiplication and an output of the previous complex multiplication delayed by one modulation interval T. The separate results from the sets of pairs of signal samples are summed to form a scalar whose value when consistently less than 0 indicates the presence of an S1 modem identification sequence in accordance with the CCITT S1 recommendation.

Abstract: In the echo-cancelling device of the invention new decision-error directed algorithms are developed which permit to maintain adaptivity of the echo coefficients and perform precise tracking of the far-end echo phase in a computationally efficent manner during full-duplex operation. The echo-cancelling device comprises an adjust device (40) performing the minimization of the mean-square error obtained as the difference between the signal at the output of the equalizer (Z) and the data-symbol decision (a), for providing the adjustment of the near echo estimator (20) coefficients, of the far echo estimator (22) coefficients, and of the phase (26) of the estimated far echo.

Abstract: For a modem receiver using an adaptive equalizer with fractional tap spacing, method and apparatus are disclosed for controlling the sample-timing phase. By evaluating bandedge components of the received signal in a particular way, a timing-phase vector signal is derived which is independent of the signal energy at the bandedges and of the quality of frequency separation of the filters for the bandedge signals. After an initial period, the current timing-phase vector signal is captured and stored as a reference. Thereafter, the sampling phase of the receiver is kept at its initial random value, represented by the stored reference timing-phase vector. The necessity to initially change the sampling phase in the receiver to a value which is forced by the received signal is avoided.

Abstract: An apparatus and a method for fast acquisition of the sample-timing phase in systems using partial-response signalling are disclosed. For fast initial adjustment of the timing phase, a known preamble is transmitted. During that phase, previous schemes could occasionally hang up for an extended period of time at the unstable equilibrium point halfway between the desired sampling times. The new procedure eliminates the hangup problem by introducing a hysteresis effect which greatly diminishes the probability of reversals in the once chosen direction of timing-phase adjustment. Thus, reliable adjustment of the timing phase with a much shorter preamble is achieved. The apparatus for furnishing a timing correction signal .DELTA..tau..sub.n includes a timing gradient generator portion (41) and a data sample reconstruction portion (43). The data sample reconstruction portion (43) develops a present reconstructed data sample x.sub.n from the present received signal sample y.sub.

Abstract: For adaptively adjusting the gain in a modem receiver comprising two amplifiers (15, 19), the following steps are performed: for a buffer (21), a Hilbert filter (23), and an equalizer (27), a respective energy indicator (P.sub.max.sup.2, u.sub.avg.sup.2, x.sub.avg.sup.2) is generated from the signal samples in the respective delay line. Each energy indicator is compared to an associataed upper target level (4L.sub.U, 3L.sub.P, 1.19 L.sub.X), and for the equalizer also to an associated lower target level (0.84 L.sub.X). If necessary, a gain correction factor (S) initially set to 1.0 is modified to obtain an overall gain that keeps delay line energies within desired targets. Target comparisons are made so that excess energy in the buffer or Hilbert filter result in a rapid gain reduction whereas average equilizer energy is used for slow adaptations. After a gain change, all acquired samples in the delay lines are also multiplied by the correction factor (S) so that none is lost during gain acquisition.

Abstract: For rapidly detecting a periodic training signal in a modem receiver, delay line storage (21) is provided for a signal section which is equal to one training signal period (q.multidot.M samples) plus an additional adjacent window (q.multidot.W samples). Thus, the stored signal section includes two windows (17', 19) which are offset by one training signal period and which are similar if a training signal is present. In evaluation means (41) connected to the two windows (17', 19), two auxiliary signals (z.sub.1, z.sub.2) are generated (61, 65) which represent the signal energy and the correlation, respectively, of the samples in the two windows. From the auxiliary signals, a dissimilarity metric (z.sub.3) is derived (69) and is compared (73) to a given threshold for generating an indicator signal (CYC) which becomes active when a training signal is present, i.e. when the two window contents are similar and the metric (z.sub.3) falls below the threshold. A carrier frequency offset estimate (.DELTA..sub.

Abstract: A maximum-likelihood sequence decoder is used with a partial-response signaling system for processing sequences of sampled values from a communication channel or recording device. The partial-response signals can be duobinary, dicode, or partial-response class-IV. The maximum-likelihood decoding for each sequence can be based upon a two-state trellis. Instead of two survivor metrics for two states, only a difference metric is necessary.

Abstract: A microprocessor having a single common data bus (17) to which the output (33) of the arithmetic-logic unit (11) as well as input and output of the data memory (13) are connected without intermediate buffer registers. Of the working registers (21, 23, 25, 27) connected to the ALU inputs, one group (21, 23) is loaded from the common data bus and the other group (25, 27), used as accumulators, is directly loaded from the ALU output. Specific control circuitry (51, 53, 55, 57, 59, 61) allows selective storing of ALU output values into accumulators (25, 27), and simultaneous transfer with selective scaling into another register and into an addressed memory location within the same cycle during which the instruction was executed.

Abstract: A maximum-likelihood sequence decoder is used with a partial-response signaling system for processing sequences of sampled values from a communication channel or recording device. The partial-response signals can be duobinary, dicode, or partial-response class-IV. The maximum-likelihood decoding for each sequence can be based upon a two-state trellis. Instead of two survivor metrics for two states, only a difference metric is necessary.

Abstract: A communication method and arrangement are disclosed which provide, for a trellis encoding process in the transmitter and a maximum-likelihood decoding process in the receiver, an additional fifth state (ZS) in addition to the usual four coding states (S0 . . . S3). The fifth state is entered in the transmitter at the end of transmission when a particularly selected escape symbol from a set of four escape symbols (E0 . . . E3) each associated to one of the four normal coding states is sent by an encoder supplement (15). In the receiver, a stop signal indicating end of transmission is only generated when, after the usual decoder delay, a path decoder (63) determines that an escape symbol was received, and a trellis decoder (61) indicates the fifth state (ZS) to be the most probable one. This enables rapid and secure determination of the end of a transmitted sequence without the need for additional transmission symbols or decoder cycles.