Abstract: A transversal adaptive finite impulse response (FIR) filter is modified for automatically filtering modulated signal components from a received signal based on frequency modulation rate. Coefficients of the filter are adapted to provide for filtering of signals having undesired modulation rates. The adapting operation includes selectively updating the coefficients using an error signal and iteratively decaying all the coefficients towards zero. The adaptation of the filter coefficients ensures symmetrical coefficient growth and introduces a constant group delay to the received signal to provide for filtering of complex signal components from a received signal according to frequency modulation rate without the use of a reference source.

Abstract: In a transmission method for simultaneous synchronous or asynchronous transmission of K data sequences consisting of data symbols, before transmission a specific signal form allocated to the data sequences is modulated on each of the data symbols of the K data sequences transmitted via a channel or K generally distinguishable channels, in order to generate the K transmission signals, which are all distorted by the one channel, or one of the K channels. In the receiver, continuous-valued provisional estimated values are calculated for some or all of the data symbols of the K input sequences according to a linear method, and a confidence level for the estimated values is calculated.

Abstract: A filter circuit largely reducing electric power consumption compared with a conventional one, as well as realizing the initial acquisition in high enough speed. In a filter circuit according to the present invention, a matched filter and a sliding correlator are used in parallel; the first acquisition and holding is executed by a matched filter, a correlating operation is executed by a sliding correlator and a voltage supply to the matched filter is stopped.

Abstract: A method for transmitting a communication signal (20) having a data rate over a plurality of spread spectrum traffic channels includes determining a first number of traffic channels required to transmit the communication signal at the data rate, and determining a second number of traffic channels (502) available for transmitting the communication signal (20). In response to a comparison of the first number of traffic channels to the second number of traffic channels, a first traffic channel (54) for transmitting a first portion of the communication signal (50, 51) and a second traffic channel (56) for transmitting a second portion of the communication signal (52, 53) are selected from the. second number of traffic channels (502). The selection of the first traffic channel (54) is non deterministic of the selection of the second traffic channel (56).

Abstract: The present invention involves demodulating a signal in a spread spectrum multiple access system employing a pilot on the forward link. The rake receiver separates the signal processing based on the period over which the processing occurs. Symbol rate processing is performed by a single time-shared multiply-accumulate datapath that services multiple finger front ends and a searcher front end. The front ends are dedicated circuits that perform all chip rate processing, producing a data vector and asserting a flag indicating the results are ready to be serviced by the shared datapath. A datapath controller arbitrates use of the datapath between the finger front ends, the searcher front end, and combining functions, configuring the datapath to service them on a first-come, first-serve basis. The controller sequences the datapath through a fixed routine as dictated by the signal processing associated with the block being serviced.

Abstract: A radio link system in which a fixed radio connection is established between two radio link terminals. The radio link terminals transmit alternately at the same radio frequency. Each of the radio link terminals includes (a) a baseband modulator in the transmitting branch for generating baseband modulation signals from a digital data stream; (b) a demodulator in the receiving branch for generating a baseband data stream by demodulating baseband signals to be received; (c) a common quadrature mixer and a local oscillator for forming an RF transmitting signal directly from the baseband modulation signals to be received directly from the RF signal to be received; and (d) a timer for connecting the radio link terminal alternately to a transmitting and receiving mode. The transmitting and receiving branches are separated at the baseband.

Abstract: A intelligent power management apparatus for use with a matched-filter. A multiplexer multiplexes shifted-in-phase chips and shifted-quadrature-phase chips from an in-phase-shift register and a quadrature-phase-shift register, respectively, to generate multiplexed chips. The multiplexed chips include alternating sets of shifted-in-phase chips and shifted-quadrature-phase chips. A controller generates a POWERDOWN signal when the multiplexed chips from a received-spread-spectrum signal do not have a particular-chip sequence. The controller generates an ACTIVATION signal when the multiplexed chips have the particular-chip sequence present. An adder tree generates a CORRELATION signal when the multiplexed chips have the particular-chip sequence and match or correlate with the settings of the adder tree. A number of AND gates inhibit the multiplexed chips from passing to the adder tree when the POWERDOWN signal is present, and pass the multiplexed chips to the adder tree when the ACTIVATION signal is present.

Abstract: The present invention concerns an apparatus and method for reducing the multiuser-interference of input signals. The apparatus in accordance with the present invention comprises a multivariate predictor (81) and a decision quantizer (82), said multivariate predictor (81) operating on interference signals .eta.'(D) provided by means for extracting interference signals (83), said interference signals .eta.'(D) being obtained from said input signals and output signals b(D) which are available at an output of said decision quantizer (82) and fed back from there to said means for extracting interference signals (83).

Abstract: An adaptive abort criterion in iterative decoding of transmitted, multi-dimensionally encoded information employs the relative entropy, approximations of the relative entropy or quantities similar thereto as criterion for the change in the weighted decisions of successive iteration sub-steps. When an iteration sub-step does not produce a change of the relative entropy lying above a predetermined threshold, then the iterative decoding is aborted.

Abstract: A receiver for transmitted signals which represent digital symbol values includes a low-pass filter to minimize transmission noise by reducing the receiver bandwidth. However, this creates pulse distortion which can cause intersymbol interference when the filtered signal is supplied to a symbol detector. Such interference is minimized by the inclusion of a feedback loop between the output of the symbol detector and the input to the filter, in which a detected symbol is multiplied by correction factor and supplied to a subtractor where it is subtracted from the signal to be filtered. The result of the subtraction is supplied to the filter. The noise reduction filter is thus also used for matching the intersymbol distortion characteristic of a filtered detected symbol to the intersymbol distortion characteristic of a filtered received signal pulse.

Abstract: A synchronizing method and circuit accurately and stably operates a direct spread spectrum multiple access communication system. A signal transmitted by modulating the spreading code with data at the transmission side is sampled by a signal of n times (n: 1 or larger integer) the clock speed of the spread spectrum signal at the reception side, and the correlation is detected by a digital matched filter. Consequently, the detection output in every sample in the symbol period is compared with the envelope detection output determined in every sampling period, and the sample positions for a specific number of determined samples are stored in the descending order of the output. The number of times of storage of large sample positions in the stored detection output is counted in every symbol period, and the position of the largest number of storage times is detected as the peak position. From this peak position, capturing or holding the symbol period and setting of the reception window position results.

Abstract: A dual-mode digital communication system for communicating an information signal during operation in frequency-modulated (FM) and multiple-access modes is disclosed herein. The digital communication system includes a dual-mode transmitter for transmitting the information signal using an FM communication signal during FM mode operation, and for transmitting the information signal using a multiple-access communication signal during multiple-access mode operation. The communication system further includes a dual-mode receiver for receiving the FM communication signal during FM mode operation, and for receiving the multiple-access communication signal during multiple-access mode operation. Incorporated within the dual-mode receiver is a digital demodulator for recovering the information signal from the received FM signal during operation in the FM mode, and for recovering the information signal from the received multiple-access signal during multiple-access mode operation.

Abstract: An apparatus and method for receiving spread spectrum signals, and, further, for decoding phase encoded information from such signals, requires correlation of input signals into real and imaginary components and determination of the phase angles of the received signal. A transmitter can divide an input signal into a plurality of data streams, independently modulate these streams, and then superpose the plurality of resultants for transmission. A receiver can receive the superposed signal and separate it into real and imaginary parts. In one embodiment, the receiver uses a plurality of spread spectrum codes to generate a plurality of real correlation signals and a plurality of imaginary correlation signals. A transmitter may also generate a differentially phase encoded signal. Phase encoding of a signal generally involves the imposition of known phase changes in the transmitted signal at selected intervals. Decoding of the phase changes at the receiver allows recognition of the phase encoded information.

Abstract: A technique for modulating and demodulating CPM spread spectrum signals and variations of CPM spread spectrum signals. A transmitter divides a signal data stream into a plurality of data streams (such as I and Q data streams), independently modulates the I and Q data streams using CPM or a related technique, and superposes the plurality of resultants for transmission. A receiver receives the superposed spread spectrum signal and simultaneously attempts to correlate for a plurality of chip sequences (such as I and Q chip sequences), and interleaves the correlated I and Q data streams into a unified signal data stream. In one embodiment, the receiver separates the received spread spectrum signal into real and imaginary parts, attempts to correlate both real and imaginary parts for a plurality of chip sequences, and combines the real I, real Q, imaginary I, and imaginary Q signals into a unified signal data stream.

Abstract: A technique for modulating and demodulating CPM spread spectrum signals and variations of CPM spread spectrum signals. A spread spectrum transmitter includes a chip sequence generator for generating a chip sequence from a data stream, a switch for dividing said chip sequence into an odd chip sequence and an even chip sequence, and a modulator for generating and transmitting a continuous phase modulated signal from said odd chip sequence and said even chip sequence. A spread spectrum receiver comprises a plurality of non-coherent serial CPM correlators, each generating a correlation signal. In a preferred embodiment, the chip sequence generator of the transmitter comprises a table of symbol codes, each symbol code comprising a series of chips corresponding to a unique series of bits in said data stream, and each non-coherent serial CPM correlator is configured to detect one of the symbol codes.

Abstract: Power control in a spread-spectrum communication system takes place by dynamically adjusting the step-down size of a power control threshold (409, 413) based on an acquired number of poor-quality frames (405). The step-down size of the threshold is increased (413) or decreased (409) depending on an amount of frame erasures detected by the system. Additionally full-rate or sub-rate frame quality is used to dynamically adjust the step-down size of a power control threshold.

Abstract: A system for publishing data on shared broadcast channels using spread-spectrum techniques, which may comprise a spread-spectrum encoder capable of receiving data and placing it in a spread-spectrum signal format and a transmitter operating on a shared communication channel or frequency band, such as might be allocated to terrestrial point-to-point or broadcast communications. The shared communication channel may comprise a cellular system, in which data may be transmitted using spread-spectrum techniques using the transmitters and repeaters of the cellular system simultaneously with voice and other transmissions associated with the cellular system. A subscriber station may be capable of receiving using a plurality of different communication channels or frequency bands, such as a first receiver capable of cellular reception and a second receiver capable of satellite reception, at least one of which uses spread-spectrum techniques.

Abstract: Each complex signal sample a(k)+jb(k) of a frequency modulated signal is limited in order to reduce co-channel interference. The limiting is performed efficiently in a digital signal processor by determining a ratio r with a magnitude less than one, equal to b(k)/a(k) in a first case and a(k)/b(k) in a second case, determining from a look-up table a variable p with a magnitude equal to 1/.sqroot.1+r.sup.2 , and determining a number equal to sgn(a(k))p(1+jr) in the first case and sgn(b(k))p(r+j) in the second case as the limited output signal sample.

Abstract: An apparatus is disclosed which is adaptable for indicating communication failures and eliminating an undesired pattern of physical values of a generated signal, the signal having physical values responsive to a sequence of information. The apparatus includes a protocol sequencer, responsive to the sequence of information and to the communication failure indications, and providing RESET and RETRY control signals; a framing flag generator, responsive to the RESET signal and providing a variable length framing flag, the length of the framing flag being dependent on the RETRY signal; a multiplex switch, responsive to the RETRY and RESET signals for generating a concatenation of the framing flag and sequence of information; a whitener generator, responsive to the RESET signal, for providing a known sequence of values; and a multiplier, for multiplying said concatenation of said framing flag and the sequence of information with the known sequence of whitener values.

Abstract: A receiver of a direct spread spectrum communication system with a window filter implemented to provide a portion of a correlation signal to a window peak detector while the complete correlation signal is being provided to a peak detector. The receiver demodulates data received in the spread spectrum signal by determining phase position information in response to peak detection signals generated by the peak detector and the window peak detector.