Abstract: A modulation/demodulation system and method comprising transmitting structure having first and second PN generators which produce distinct, synchronized, first and second PN sequences. A tapped delay line generates a plurality of symbols from the second PN sequence, each symbol corresponding to an offset of the second PN sequence by one or more chips from the epoch of the first PN sequence. A plurality of output taps are associated with the tapped delay line, with each tap corresponding to one of the symbols. A symbol selection device associated with the output taps selects from amongst the symbols based upon one or more message signal bits. The selected symbols and first PN sequence are applied to separate channels of a modulator to modulate a carrier signal. At a destination, first and second local PN generators generate first and second PN sequences which correspond to the first and second PN sequences in the transmitting structure.

Abstract: In a satellite mobile telephone a radio signal is transmitted by firstly generating (602) a digital input signal. The digital input signal is processed (703) in combination with a digital modulating signal (704) to produce a digital intermediate signal. The digital intermediate signal is converted (705) into an analog intermediate signal and said analog intermediate signal is processed (706) in combination with an analog modulating signal to produce a radio frequency output signal. Similarly, during reception, a received signal is processed in combination with an analog demodulating signal to produce an analog intermediate signal. The analog intermediate signal is sampled to produce a digital intermediate signal and said digital intermediate signal is processed in combination with a digital demodulating signal so as to select a transmitted channel.

Abstract: A method for reducing interference and increasing spectral efficiency in a frequency reuse pattern (600) is disclosed. The method includes the steps of generating n original communications beams (302-308) assigned to substantially non-overlapping frequency bands, with the original communications beams extending over a first set of predetermined bandwidths. The method also generates n shifted communications beams (402-408) shifted by an orthogonal frequency separation from the n original communications beams (302-308), with the n shifted communications beams (402-408) extending over a second set of predetermined bandwidths. The method projects the n original communications beams (302-308) and the n shifted communications beams (402-408) in a frequency reuse pattern (600) over a region of interest by alternating the n original communications beams (302-308) with the n shifted communications beams (402-408).

Abstract: A method for a wireless discrete multitone spread spectrum communications system, synchronizes the remote station to the base station. The method begins with the step of generating a clock signal at the base station. The base station then derives a synchronization symbol pattern from the base station clock signal and spreads the it with spreading codes that distributes the symbol pattern over a plurality of discrete tones, forming a discrete multitone spread spectrum signal. The base station then transmits the spread signal to the remote station. The remote station generates a first clock signal and samples the discrete tones using the remote station first clock signal, forming a first sampled signal. Then the remote station applies the first sampled signal to a matched filter bank, forming a frequency error signal. The method then adjusts a frequency of the remote station first clock signal using the frequency error signal, forming a second clock signal.

Abstract: In a first embodiment of the invention, two sets of seven PN-sequences of length 128 are provided having favorable correlation properties for use as a preamble or midamble synchronization code. At the receiver a processor may be used to detect the code. In another aspect of the invention, a communication system using a synchronization code selected from sets of provided codes is claimed where the synchronization code may help to minimize possible misidentification of noise or interference by assisting in the detection of the start of a designated burst. The synchronization codes and their means for detection may be employed in various communication systems.

Abstract: A packet data transmission system is disclosed in which remote units, such as remote hand-held data gathering units, which normally communicate with remote base stations via a spread spectrum RF communications, are initialized via spread spectrum RF communications. A network chipping sequence is provided for encoding normal communications and an universal chipping sequence is provided for encoding communications relating to initialization of the remote units. The network chipping sequence is adjustable and must be initialized in each of the remote units to enable normal communications. The universal chipping code is fixed for all remote devices and base stations. Since the universal chipping code is fixed, spread spectrum RF communications of the initialization data, using the universal chipping code, can be effected even if the network chipping sequence is not initially set in the remote units.

Abstract: A device and a method for aligning in time two essentially isochronous digital signals are provided, in which a plurality (2.sup.n) of replicas (CK1-CK4) of the first signal (CKIN), separated by a given phase difference, are generated and a number of said replicas (CK3, CK4) is subjected to sampling (4, 5) in correspondence with the rising edges of the second signal (DATA). As the result of the sampling, a combination of logic signals (SL0, SL1) is obtained which is representative of the phase relation existing between each of said replicas (CK1-CK4) and the second signal (DATA). The output signal (CKOUT) of the device, aligned with the second signal, corresponds to the one, among the replicas (CK1-CK4) of the first signal, which best reproduces the desired alignment condition.

Abstract: A system is disclosed for permitting a mobile telephone to recover an ongoing communication following a temporary interruption of operation, e.g., such as caused by an interruption of power to the mobile telephone, which includes circuitry and processor control to calculate the duration of the temporary interruption and for restoring synchronization of the mobile telephone to the mobile communication system. The circuitry stores synchronizing information prior to the temporary interruption and cycles synchronizing circuitry of the mobile telephone at a higher than normal cycling rate to restore synchronization of the mobile telephone with the mobile communication system. In a further embodiment, circuitry is disclosed for restoring the output of spread code generating circuitry in a spread spectrum digital mobile telephone to a phase used by a transmitting station of the mobile communication system.

Abstract: There is provided a method of transmitting and receiving a frame including unique pattern information indicative of a starting point of digital information. Step (a) performs a receive synchronizing process in which the frame is pulled in a given phase of a machine cycle equal to m which is equal to (1/N).times.L where L denotes the number of bits forming the frame, N is a positive integer and m is a positive integer larger than 2. Step (b) performs, in a receive process executing phase forming part of a same machine cycle as that of the step (a), a receive process in which receive control channel data contained in a received frame is written into a shared memory in accordance with first m-bit stream program information which defines the receive process and is stored in the shared memory.

Abstract: A method and apparatus for providing equalization for a communication channel is provided. The invention uses edge transition samples, such as those obtained for phase detection in a phase locked loop (PLL) circuit, to determine the amount of equalization to be applied to signals received from a communication channel. By monitoring run lengths of consecutive identical bits received from the communication channel, the invention provides equalization for various frequency components present in the receive signal. One embodiment of the invention subtracts a weighted RC-filtered version of the receive signal from the unfiltered receive signal to provide an equalized receive signal. In this embodiment, a control circuit that monitors the received run lengths and edge transition information adjusts the resistance of the RC filter to adapt the equalization to the data being received and the potentially time varying conditions for the communication channel.

Abstract: A pattern detector adapted for wireless communication systems includes an error calculator, a comb filter, an averager, and a threshold detector. The pattern to be detected is a sequence of pilot signal patterns whose error calculation is relatively invariant with respect to frequency offset introduced by Doppler and the local oscillator. The pattern detector processes received input samples y.sub.k to determine an error signal from the input samples y.sub.k and estimated input samples y.sub.k. The estimated input samples y.sub.k are determined using an estimated channel impulse response. When a vector of the received input samples is "aligned" with the expected header sync input samples, the level of the error signal is about equal to the level of the noise. The pattern detector determines the average level of the error signals for the last K error signals of each sample position E.sub.

Abstract: The present invention relates to a method for setup of a signal in multicarrier modulation, including clipping the signal, in amplitude, with respect to a threshold value, and of reinjecting, with a delay and on the signal to be set up, a clipping noise redistributed, at least partly, outside the useful slip of the signal in multicarrier modulation.

Abstract: A digital radio communications system including a suboptimal soft decision (e.g., errors and erasures) channel decoder and a speech decoder can be upgraded to effectively bypass the hard decision channel decoder and allow a higher performance soft decision (e.g., maximum likelihood sequence estimate (MLSE)) decoder to be used--without requiring physical removal or disconnection of the hard decision channel decoder. The new decoder can feed the existing decoder the right choice of received vector r' to force the existing decoder to produce a certain codeword y' and a certain bit error estimate b'. This technique is useful to test new MLSE decoders on existing radios, or to add an MLSE decoder as an upgrade on existing receivers.

Abstract: The present invention relates to a system for directly connecting two PC modems over dry copper, for the purpose of accessing an outside provider of computational services, substantially as though the connection were provided by the telephone network services. In preferred embodiments, both modems follow the V.90 specification, and are connected through an analog front end which emulates some components of the digital telephone network services. In another preferred embodiment, the present invention enables a group of private users in a contained community of one or more adjacent buildings, each with a PC modem, to share a higher speed digital line, such as an ISDN for example, for the purpose of providing a more economical access to a computational service.

Abstract: There is disclosed in a frequency hopping digital communication network having a multimode radio transmitter for transmitting a data signal and a multimode radio receiver tuned for receiving the same, the multimode transmitter and receiver operable in a first standard mode and a second enhanced mode, each mode having a late-net acquisition library period and an in-net acquisition library period, a method for obtaining a non-noisy frequency channel over which to receive the data signal transmitted across the radio network. The method comprises the steps of successively averaging signal samples received over a particular frequency channel and time interval corresponding to the receiver mode and library period to determine the noise level of the particular reception frequency channel. The averaged signal samples are then compared to a predetermined noise threshold to determine whether the frequency channel is noisy.

Abstract: In an FSK modulated signal receiving station a synchronization sub-system is arranged to sample the received signal and to select one sample per symbol within a detection window having a finite length, said samples being selected at predeterined instants. This produces a number of versions of the sampled signal and these different versions of the signal are then processed in parallel to determine the signal timing and the signal frequency offset.

Abstract: The present invention is an apparatus and method for detecting a codeword from a data stream comprising a series of sequences of samples representing intensities of an analog signal. The data stream may be output from, for example, a holographic storage device. The data stream is encoded using a code which may be represented by a trellis. One embodiment of the present invention uses a block encoded balanced code, one embodiment uses a finite state encoded balanced code and another embodiment uses a finite-state encoded DC free code. Each code defines a set of codewords which meet the constraints of the code. The codewords are detected from a sequence of samples by selecting the codeword having the greatest correlation with the sequence of samples. In a preferred embodiment, the correlation detection is implemented using the Viterbi process to iteratively determine correlations and codewords for each state at each level of the trellis based on the correlations at the preceding level of the trellis.

Abstract: A unit of the invention is installed in each of transmission units that make up a synchronous network. The unit selects from the clock references received an active reference that controls the operation of the corresponding transmission unit, based on the quality levels of clock references presented by synchronization messages received with the clock references. The clock references, each of which is selectable as the active reference, and their selection priorities are entered into a source priority list. By referencing the source priority list, the active reference is selected.

Abstract: In a transmission system a sequence of digital symbols including concatenated words, is transmitted by a transmitter (2) via a transmission medium (14) to a receiver (16). In order to reduce the transmission capacity no word synchronizing symbols are introduced in the sequence of digital symbols. In order to achieve word synchronization, a synchronization processor estimates the probability function of one single predetermined string as function of the position of the string in the sequence. The correct position of the words is derived from this probability function.

Abstract: A system and method for applying channel weights in a communication system are presented. The application of weights derived from a sample window is time-shifted into that sample window, decreasing the effects of channel variation and partially compensating for degradation due to differential detection.