Abstract: A digital filter method comprising the following steps: input signal data x(n) is sampled at sampling frequency Fe and shared between and stored in Q memories of shift register of FIFO type associated with the Q branches of the filter. The filter coefficients g.sub.m (p) are stored in at least one other memory referred to as a "coefficient" memory. Interpolation by L followed by decimation by M makes it possible to reduce the working frequency of the filter to the output frequency Fs=(L/M)Fe with L/M<1. Data samples x(n) are multiplied by the coefficients g.sub.m (p) at the rate Fs. According to the invention, the data samples x(n) in each branch remain present for a plurality of multiplications .apprxeq.Fe/Q, and the coefficients are rotated in each branch by address permutation in the coefficient memory at each clock period. The invention proposes various devices implementing the method. Applications in radar and in telecommunications.

Abstract: A method and apparatus for time division duplex (TDD) repeating a spread spectrum signal, where spread spectrum signal is comprised of a series of code symbol modulated with a pseudonoise (PN) sequence. The TDD repeater receives intermittently the spread spectrum signal at a location remote from a source supplying the spread spectrum signal. The TDD repeater amplifies and delays the received spread spectrum signal by a predetermined amount. The TDD repeater transmits intermittently the delayed amplified received spread spectrum signal such that the TDD is not receiving the spread spectrum signal when it is transmitting the signal energy.

Abstract: An adaptive equaliser particularly for equalising digital signals with analogue modulation, where use is made of a training sequence formed by a previously known sequence of symbols which is applied to said equaliser simultaneously with the demodulated signal present in the receiver. In this way a first estimate is made of the coefficients of the filter or filters of the equaliser that compensate the linear distortions in the transmission channel. The training sequence (TS), before being used in the equaliser (CEQ), is first applied to a lowpass filter whose transfer function is the same as that of the premodulation filter employed in the modulator. This transfer function also incorporates distortion effects, both linear and non-linear, to which the data are subjected in the receive side when they have been demodulated prior to their detection or regeneration.

Abstract: An apparatus and process for improving the performance of a cellular communication system using direct sequence spread spectrum techniques is disclosed. The apparatus and process enable dynamic modification of communication system parameters including PN code length, chipping rate and modulation technique for transmission of a data packet. Modification is based on proximity of the transmitter and receiver, noise level, transmitter and receiver capabilities and other factors. The system makes tradeoffs between data transmission speed and communication range to improve system performance.

Abstract: A system and method for communicating information using circular multidimensional signal space constellations using uncoded modulation allows increased data rate and bandwidth by eliminating trellis encoding, thus reducing the number of computational cycles required for coding. Furthermore, the use of circular signal space constellations lowers the transmit peak factor, thus consuming less power. Using uncoded modulation with circular constellations allows an approximate 10-20% performance improvement for a given central processor unit. Additionally, circular constellations allow the easy and reliable transmission of special marker symbols such as "End of File", "Start of Message", "End of Transmission" or "Increase or Decrease Data Rate".

Abstract: A data communications system characterized by the combination of a base station connected to a plurality of repeaters for communicating with remote terminals in response to outgoing data from a host computer and for communicating with the host computer in response to incoming data from the remote terminals. Each repeater is assigned a coverage area with in a predetermined communications area to support data communications with the remote terminals located within its coverage area. In response to incoming data, a repeater conducts a signal amplification operation and outputs amplified incoming data to the base station via a first communications link. The base station processes the amplified incoming data and, in turn, generates processed incoming data for distribution to the host computer via a second communications link.

Abstract: A direct sequence spread spectrum (DSSS) system which uses PN sequences to encode data so as to increase data throughput. In particular, a system for communicating a plurality of data values using multiple spreading sequences is provided. The system transmits data by selecting at least one of the multiple spreading sequences based on at least one data value included in the plurality of data values; and transmitting other data values included in the plurality of data values using the at least one of the multiple spreading sequences to spread the other data values.

Abstract: At the transmitter side, carrier waves are modulated according to an input signal for producing relevant signal points in a signal space diagram. The input signal is divided into, two, first and second, data streams. The signal points are divided into signal point groups to which data of the first data stream are assigned. Also, data of the second data stream are assigned to the signal points of each signal point group. A difference in the transmission error rate between first and second data streams is developed by shifting the signal points to other positions in the space diagram. At the receiver side, the first and/or second data streams can be reconstructed from a received signal. In TV broadcast service, a TV signal is divided by a transmitter into, low and high, frequency band components which are designated as a first and a second data stream respectively.

Abstract: A method and apparatus for reducing noise correlation in a partial response channel through optimization of a look-ahead maximum likelihood (ML) detector. In the method of the present invention, the ML detector is optimized in light of the noise correlation generated by the partial response channel. The improved ML detector provides comparable performance to, or better performance than, a Viterbi detector in the presence of colored noise. In the present invention, a set of finite impulse response (FIR) transversal filters are used as the ML estimator for the look-ahead detector. The weighted sum outputs of the FIR filters are compared to a set of thresholds based on previously detected data to make the decision for current detection. The present invention improves the ML detector's performance and reduces its complexity by optimizing the coefficients of the FIR filters in the presence of the correlated or colored noise.

Abstract: The invention provides an automatic amplitude equalizer for compensating an amplitude characteristic of an input signal, wherein a control signal for equalizing an inclination amplitude distortion of an input signal is detected making use of a pair of digital demodulated signals to compensate for the amplitude characteristic of the input signal with a high degree of accuracy and which can be constructed with a reduced circuit scale and at a reduce cost.

Abstract: A method and system for alerting a mobile terminal in a high-attenuation propagation environment within a mobile satellite communication network are disclosed herein. The method comprises receiving an incoming call directed to the mobile terminal, generating a paging signal in response to the incoming call, determining whether the mobile terminal has failed to receive the paging signal, and generating an alerting signal in response to the determination that the mobile terminal has failed to receive the paging signal.

Abstract: A Viterbi decoder generates a branch metric table from first and second data signals taken at two sample times and provides selected branch metrics to an add/compare/select circuit in response to branch indices from a branch index generator. The branch metrics in the branch metric table are the sixteen combinations of the sum of the first and second parallel data signals at first and second sample times and the inverse of such signals. The branch index generator generates the branch indices in response to a received state from the add/compare/select circuit, convolutional code polynomials and the possible states of a radix-4 trellis. The add/compare/select generates a survivor path decision based on the selected branch metrics.

Abstract: A pilot signal detection method, a pilot signal detection apparatus and a subscriber in which the timing of a pilot signal of a neighbor base station is detected correctly and efficiently for improving the quality of communication of a mobile station. Partial correlation is taken of a pilot signal of an arbitrary base station within a first range of correlation. The pilot signal for which the result of the partial correlation has exceeded a first threshold becomes a pilot candidate signal for detection. Partial correlation is then taken of the pilot signal of the pilot candidate signal within a range of correlation broader than the first range of correlation. The pilot signal for which the result of the partial correlation has exceeded a second threshold becomes a pilot detection signal.

Abstract: An apparatus for serial data communication between a plurality of IC chips with a reduced number of inter-chip signal lines. In the apparatus, one IC chip acts as a master, while the other chip(s) are slaved to it. In response to conditions internal to the master chip or in response to a request from at least one of the slave chips, the master chip generates a transfer control signal and a synchronization clock signal. The transfer control signal defines a transfer phase during which data transfer among the chips can take place. The chips take turns sending and receiving data in a multiplexed fashion, with sending and receiving parties designated by a count of synchronization clock signal cycles. The synchronization clock signal is generated at a high frequency, to allow fast data transfer.

Abstract: A transmitter of a spread spectrum communication system includes a data generating portion, a differential coding portion, an S/P converting portion, multipliers, PN generator, a local signal generator, modulators, delay elements, combiner, a frequency converting portion, a power amplifying portion and a transmission antenna. Parallel signals are multiplied by a spread code from the PN generator, and the results are delayed by delay elements and multiplexed. Time difference between the delay times are set to an arbitrarily time period of at least 1 chip from each other. Therefore, error rate characteristics can be improved, and degradation of correlated output is suppressed, whereby difficulty in demodulation can be avoided.

Abstract: A coherent dual-channel QPSK modulator/demodulator for a CDMA system, and modulating/demodulating methods therefor, are disclosed, in which the crosstalk interferences between an I-channel and a Q-channel are eliminated by an orthogonal spreading method, which assigns different Walsh codes to the I-channel and Q-channel. Pseudo-random modulation and pseudo-random demodulation are carried out by using one PN code so as to minimize the channel parameter estimation errors, thereby improving receiving performance.

Abstract: A process for transmitting data selects sample values that represent data symbols and then converts the sample values to voltage levels in a transmitted PAM signal. A receiver samples the PAM signal and identifies the data symbols from the sampled voltage levels. At least some of the data symbols have multiple alternative representations; and for a data symbol having multiple alternatives, a sample value is selected to reduce low and high frequency components in the PAM signal. Accordingly, the PAM signal carries less information at low and high frequencies and is less disturbed by transformers, low pass filters, and local loop impairment in the transmission channel. The process for selecting sample values determines a weighted average of the lowest and highest frequency components. The weighting of the average can be selected according to a measured frequency response of the channel during initialization.

Abstract: A digital data receiver includes a tunable analog matched filter circuit having a variable bandwidth responsive to the bit error rate (BER) of the decoded data. The bandwidth of the analog filtering circuit is controlled by a tuning control signal that includes a coarse tuning signal combined with a fine tuning signal. The coarse tuning signal is generated by a frequency-to-current converter and the fine tuning signal is generated by a current-scaling digital-to-analog converter (DAC). The DAC input signal is produced by a DAC control circuit that includes a BER comparator and a DAC control state machine. The BER comparator determines whether the BER has improved or degraded in response to a previous tuning command. To optimize the BER in the decoded data signal, the state machine increments or decrements the value of the fine tuning signal, which in turn alters the filter bandwidth.

Abstract: A data communication apparatus includes a modem for determining a line quality and setting a transmission baud rate and a transmission bit rate in accordance with a result of the determination, and a control circuit for changing setting criteria of the baud rate and the bit rate of modem in accordance with the data received from the line through modem.

Abstract: A memory efficient time de-interleave, de-puncture and viterbi decoder circuit is provided for decoding frames of digital data that is time interleaved over a plurality of data frames, wherein the time interleaved digital data includes convolutionally encoded data. The circuit includes a time de-interleave block having an input receiving a stream of the digital data and an output connected to an input of a de-puncture block, which has an output connected to an input of a viterbi decoder block. The time de-interleave block is adapted for communication with an external memory wherein the time de-interleave block establishes a plurality of address pointers thereto corresponding to the plurality of time interleaved data frames. In accordance with the address pointers, the time de-interleave circuit stores the viterbi metric data for a number of data frames within the external memory in a storage efficient manner.