Abstract: A correlation value calculating apparatus reduces the calculating time with respect to the whole phase range.

Abstract: A comb limiter combiner for frequency-hopped communications includes an input signal coupler for coupling to a receiving antenna and distributing the antenna signal to a bank of input bandpass filters. The input bandpass filters have contiguous passbands that comprise the total receiver bandwidth. Each input bandpass filter is connected to a limiter having a threshold substantially equal to the limiting threshold of the receiver. Each limiter is connected to an output bandpass filter similar to the corresponding input bandpass filter to remove out-of-band intermodulation products generated by the limiter. The bank of output bandpass filters is connected to an output signal coupler for coupling to the front end of the receiver.

Abstract: A multiple description TCQ arrangement employs a trellis graph that is the tensor product of two trellis graphs. The codevectors of the tensor-product trellis, ci, are incorporated within trellis graph T1 and also within trellis graph T2. The incorporation within trellis graph T1 is effected by assigning the ci codevectors to sets, and by deriving therefrom codevectors for trellis graphs T1 and T2. The actual values that these codevectors take on are arranged to insure certain distortion results. Consequently, an improved arrangement is realized in which, two encoders are cooperatively generating separate trellis-coded descriptions of the input sequence. Three different fidelity levels can thus be achieved, which allows for use of receivers that are responsive to different rates, or the use of receivers that have adaptable rates.

Abstract: A radio receiver for vestigial sideband digital modulation, such as used for transmitting digital television signals, employs real-only digital synchrodyne circuitry for synchrodyning a real digital carrier with digitized final intermediate-frequency signal to generate an in-phase synchronous detection signal. Digital filtering supplies a complex frequency response to the digitized final intermediate-frequency signal. Further digital synchrodyne circuitry synchrodynes this complex frequency response with a complex digital carrier to generate a quadrature-phase synchronous detection signal. This quadrature-phase synchronous detection signal is used in automatic frequency and phase control of a local oscillator used in the conversion of received signal to the final intermediate-frequency signal for digitization.

Abstract: A multilevel coded modulation scheme is provided in which a first portion of input data is encoded by a first-level code and a second portion of input data is encoded by an second-level code, the second-level code being such that the overall multilevel code exhibits a desired level of time diversity of at least 2 and the minimum distance of the overall code is not increased by virtue of the presence of the second-level code.

Abstract: A digital signal communication system includes a transmission circuit or a receiving circuit for digitally transmitting two types of signals by orthogonal modulation. The transmission circuit includes an orthogonal modulator and a nonrecursive digital low-pass filter having the same frequency characteristic as a predetermined frequency characteristic of the output signal of the orthogonal modulator. The receiving circuit includes an orthogonal demodulator and a nonrecursive digital low-pass filter having the same frequency characteristic as a predetermined frequency characteristic of the output signal of the orthogonal demodulator. The total number of taps required for determining the frequency characteristic of the nonrecursive digital low-pass filter is set to H, and the series of tap coefficients is set as C1, C2, C3, . . . , CH, where H is an arbitrary positive integer of not less than 2.

Abstract: A digitally modulated RF amplifier system is presented having improved adjacent sideband distortion reduction. This system includes the provision of a first RF carrier signal at a first frequency within a first frequency channel having adjacent channels. A modulator receives a digital information signal and modulates the first RF carrier signal with the digital information signal to provide a digitally modulated RF signal within the first RF channel. A second RF carrier signal is provided having a second frequency spaced from the first frequency channel by a frequency that is greater than the bandwidth of the first channel. The digitally modulated RF signal is combined with the second RF carrier signal to provide a combined RF signal which is then amplified resulting in an amplified RF signal having reduced adjacent sideband distortion products.

Abstract: A PLL is provided for reproducing a standard clock having a constant Jitter band from a random time information.

Abstract: A correlator includes a circuit for serially receiving in phase (I) and quadrature (Q) signal data along parallel I and Q signal channels and converting the data to blocks of n bit parallel I and n bit parallel Q signal data. At least one programmable read only memory (PROM) stores I and Q reference data. The memory receives and stores within each respective parallel I and Q signal channel a current block of n bit parallel I and n bit parallel Q signal data and the immediately previous received blocks of n bit parallel I and n bit parallel Q signal data. A data bus receives the n bit parallel I and Q reference data and the n bit parallel I and Q signal data. The n bit parallel I and Q reference data are correlated with a one bit shifted version of the respective n bit parallel I and Q signal data from an adjacent previous path to produce a correlated I component signal output and a correlated Q component signal output.

Abstract: The present invention relates to an arrival direction estimation method using an array antenna and a DS-CDMA receiver unit using this method. The method produces an accurate estimate of the arrival direction of a desired signal regardless of reception level and high interference. In a DS-CDMA communication system for performing a transmission by a spreading process using a code having a period longer than a symbol length, received signals from an array antenna are subjected to a despreading process by despreading units. A cross-correlation function with time lags of the recieved signals is obtained by inverse-modulating despread output signals by a known symbol in an inverse modulator. An arrival direction of a received signal is estimated by an arrival direction estimation unit based on the cross-correlation function. A beam former combines the despread output signals depending on the arrival direction and outputs an output signal to a channel receiver.

Abstract: A sub-rate modulation method that is compatible with full-rate ADSL modems. The method may be used to implement a reduced complexity transceiver, preferably remotely located from the central office or service provider. The method includes instructing the full-rate modem to transmit data using a subset of available carriers; receiving the subset of carriers at the remote location; and performing a reduced complexity time-to-frequency domain transform. The full rate modem is instructed to use every other carrier, resulting in a transmitted time domain sequence that is cyclic—the first half of the symbol is identical to the second half. As a result, the first half of the symbol is treated as an extended cyclic prefix by the sub-rate ADSL modem, resulting in the elimination of the need to perform time-domain equalization at the sub-rate ADSL modem receiver. This substantially reduces the amount of signal processing required by the sub-rate ADSL transceiver.

Abstract: The present invention provides a method and apparatus for eliminating or reducing local area and broad area interference in a twisted pair transmission system. The apparatus of the present invention includes a detection device, such as an antenna, for example, for detecting electromagnetic interference coupled into a twisted pair line, a sampling/scaling device which samples and scales the detected signal, and a combiner device which combines a signal correction component with the signal received over the twisted pair by a differential receiver. The sampling/scaling device preferably includes an analog-to-digital converter (ADC) which converts the detected analog signal into a digital signal and a digital signal processor, which receives the digital signal from the ADC and processes the signal to generate a correction signal. The correction signal is then subtracted from the signal received by the differential receiver. The sampling/scaling device may be fixed or adaptive.

Abstract: An apparatus for filtering radio frequency interference in a signal transmitted on a twisted-pair communication channel such as an ADSL transmission line. The apparatus includes a filter adapted to be selectively engaged in-line with the communication channel by a switch or switches when the differential mode noise in any predetermined frequency sub-band exceeds a threshold noise level, or the sum of the sub-band noise signals exceeds a wideband threshold noise value. When the filter is not engaged, it is isolated from the communication channel by a bypass switch or pair of bypass switches.

Abstract: A broadcasting method for simultaneously broadcasting analog and digital signals in a standard AM broadcasting channel is provided by: broadcasting an amplitude modulated radio frequency signal having a first frequency spectrum, wherein the amplitude modulated radio frequency signal includes a first carrier at a frequency of f0 modulated by an analog program signal representative of program material; and simultaneously broadcasting a plurality of digitally modulated orthogonal frequency division multiplexed carrier signals within a frequency range of about f0±15 kHz, which encompasses the first frequency spectrum, each of the digitally modulated carrier signals being modulated by a portion of a digital program signal, wherein the digital signal includes a digital representation of the program material, additional data, or a combination of the program material and the additional data.

Abstract: A spread spectrum communication device having a channel estimator and a rake receiver with a number of rake fingers. The spread spectrum communication device is used in a direct sequence spread spectrum, code division multiple access system. In the spread spectrum system, symbols are spread by a pseudo-noise reference sequence, with a chip rate substantially higher than a symbol rate of the symbols, the spread symbols are modulated onto a carrier, and the carrier modulated signals are transmitted over an air-interface. The air-interface tends to produce multipath components of the transmitted signal. The spread spectrum communication device receives the multipath components, and demodulates symbols intended for it, by de-spreading the received signals with a locally generated pseudo-noise reference sequence, and coherently adding multipath resolved components intended for it.

Abstract: A digital demodulator (100) includes a differentiate and cross multiply stage (102) and a plurality of filter/decimator stages (106, 112, 118 and 108, 114, 120 and 110, 116, 122) that accept both multiple baud rates and multiple modulation deviation frequencies, and that provide a common frequency data stream at their respective outputs. One of said filter/decimator stages is coupled to a primary filter (124) which is followed by a box filter (134). The box filter (134) improves the overall filter response and provides notches at a specified frequency (e.g., 4800 Hz) and its harmonics. Demodulator (100) provides improved sensitivity without the need for any circuit trimming. The filter stages (e.g., 106, 112, 118; 108, 114, 120; and 110, 116, 122) used in demodulator (100) have been optimized to eliminate the need for costly multipliers.

Abstract: A method and/or system for stabilizing the operation of fractionally spaced equalizers has a number of taps (P), associated with which are respective equalization coefficients (c−L, . . . , cL), used in digital signal receivers, wherein the equalization coefficients (c−L, . . . , cL) are updatable to an algorithm (1) based on the minimization of a proper cost function (J) and stabilized for operation through a proper a modification (I) involving calculation of a plurality of values (Ii) to be considered in updating the equalization coefficients (c−L, . . . , cL). According to the invention, these values (Ii) are calculated in only one circuit (COMP) and serially transmitted to the fractionally spaced equalizer (FSE).

Abstract: A method and apparatus for symbol timing initialization in a multi-carrier receiver. The method uses phase measurements from a plurality of the individual carriers to make an initial determination of the symbol boundary. The method measures the phases of two carriers, preferably the pilot carrier and one adjacent carrier, and, after compensating for phase distortion associated with modulation of data onto the carrier and phase distortion imposed on the carriers by the channel, determines the symbol timing based on the phase difference between the two carriers. Because a sampling offset results in a phase offset from bin to bin of a DFT, an examination of the extent of the phase offset between two known symbols yields the sampling offset, and thus the symbol frame index.

Abstract: The architecture of the present invention is premised upon an algorithm involving integration of oblique correlators and RAKE filtering to null interference from other spread spectrum signals. The oblique correlator is, of course, based on the non-orthogonal projections that are optimum for nulling structured signals such as spread spectrum signals. RAKE filtering is used to rapidly steer the beam of the multi-antenna system and to mitigate the effects of multipath.

Abstract: The present invention provides a method and apparatus for implementing a continuous phase modulation with an approximate phase constellation. The method reduces complexity by using fewer than all phase points of the nominal phase constellation. The method includes the steps of storing (502) an approximate phase constellation of phase points (100) selected from a nominal phase constellation of phase points, identifying (504) a next phase in the approximate phase constellation of phase points using an N-bit input word, and outputting (506) the next phase. In reducing the number of phase points used in the modulation, the method may store only unique phase points in said phase constellation, and may further reduce the number of phase points by storing only those phase points differing by at least a phase threshold.