Abstract: A digital audio broadcasting (DAB) system includes a radio-frequency (RF) receiver that develops a characterization signal representative of a respective mobile communications channel as a precursor to estimating a channel impulse response. The latter is used to set coefficients of an equalizer of the receiver to compensate for distortion such as intersymbol interference. In generating the channel impulse response a Fast Fourier Transform (FFT) of the characterization signal is performed. The resulting FFT is then clipped such that frequency components above a predetermined upper threshold and less than a predetermined lower threshold are set to the respective threshold values. This allows coefficients for the equalizer to be generated such that the equalizer converges even in the presence of strong reflections in a mobile communications environment.

Abstract: A digital audio broadcasting system includes an RF transmitter and a corresponding RF receiver. In the RF transmitter, a digitally compressed audio signal is encoded into a symbol stream that is first rotated using a frequency of 150,000 hertz (hz) before transmission to the RF receiver.

Abstract: A blind equalization technique uses both the "constant modulus algorithm" (CMA) and the "multimodulus algorithm" (MMA) during blind start-up. This approach provides the basis for a "transition algorithm." One example of a transition algorithm is the CMA-MMA transition algorithm in which an adaptive filter simply switches from CMA to MMA. Other examples are variations of the CMA-MMA transition algorithm and are illustrated by the "Constant Rotation CMA-MMA" transition algorithm and the "Dynamic Rotation CMA-MMA" transition algorithm.

Abstract: A digital audio broadcasting (DAB) system includes a radio-frequency (RF) transmitter and a corresponding RF receiver that includes a frame detection circuit for providing a frame synchronization signal. The latter is used to inhibit a Reed-Solomon decoder from correcting data in any frame for which there was no synchronization.

Abstract: A blind equalization technique--the multimodulus algorithm (MMA)--adapts coefficients of an equalizer so as to minimize dispersion of the output samples of the equalizer around piecewise linear contours of a signal space. The MMA technique is illustrated in the context of both square and non-square signal point constellations.

Abstract: A personal computer (PC) incorporates a speaker/microphone peripheral, which includes a digital-signal-processor (DSP) based acoustic echo canceler and supports a plurality of modes of operation. One mode is a video/telecommunications mode. In this mode, the acoustic echo canceler is enabled and the speaker/microphone peripheral provides a monaural dual speaker and microphone for use in video, internet telephony, etc., communications. Another mode of operation is a multi-media, or wide-band stereo, mode. In this multi-media mode, the acoustic echo canceler is disabled and the stereo loudspeakers provides high fidelity stereo output signals. In addition, in this latter arrangement an optional sub-woofer may be additionally coupled to the stereo loudspeakers. The speaker/microphone peripheral switches between the operating modes by detecting a predefined sequence of dual-tone-multi-frequency (DTMF) digits. The DTMF sequences are played from wave-type files stored on the PC.

Abstract: A timing technique for a Quantization-Level-Sampling (QLS) modem puts timing information in a downstream pulsed signal transmitted from the public switched telephone network (PSTN) to the QLS modem. In response to this timing information, the QLS modem synchronizes to the network sampling clock of the PSTN. In particular, the pulsed signal includes data-bearing samples, which were provided by a far-end QLS modem, and at least one non-user-data-bearing (NUDB) sample in which the level of this NUDB sample periodically alternates. The QLS modem extracts timing information from this periodic alternating signal level to synchronize the QLS modem to the network sampling clock.

Abstract: A digital audio broadcasting (DAB) system includes a radio-frequency (RF) transmitter and a corresponding RF receiver. The RF transmitter formats a DAB signal into a sequence of frames, each frame having a header comprising a predefined grouping of psuedo-random number sequences comprising 100 symbols. Of these 100 symbols, 86 symbols of the header are used for frame synchronization and channel sounding (for characterization of a communications channel), while the remaining 14 symbols are used for interleaver and data synchronization in an interleaved fashion.

Abstract: A rail-to-rail driver amplifier circuit that utilizes complementary output transistors to fully utilize the available power supply voltage. The circuit includes an input pre-amplifying circuit for receiving the audio signal and for receiving electrical energy from a power supply having a first rail at a positive potential and a second rail at a negative potential to produce a pre-amplified output signal. The circuit further includes a first output driver circuit having a voltage gain limited current amplifier coupled to the first rail and to a first output terminal of the input pre-amplifying circuit and a second output driver circuit having a voltage gain limited current amplifier coupled to the second rail and to a second output terminal of the input pre-amplifying circuit.

Abstract: A hybrid type of decision feedback equalizer (DFE) structure that approaches optimal DFE performance is described. The hybrid DFE includes both an intersymbol interference DFE (ISI-DFE) and a noise predictive DFE (NP-DFE). In particular, an adaptive feedforward filter section is followed by both an intersymbol interference (ISI) predictive filter and a noise predictive (NP) filter. The corresponding transmitter uses a precoder that utilizes optimal coefficient values, denoted as C(z), of the hybrid DFE structure. In particular, C(z) is equal to (1+I(z)) (1+N(z))-1, where, the notation I(z) and N(z), as known in the art, represent the resulting coefficient values after adaptation of the ISI-DFE and the NP-DFE, respectively.

Abstract: In a simultaneous voice and data communications system, a voice signal is added to a data signal before transmission over the public switched telephone network (PSTN). In particular, in every signaling interval, a signal point is selected for transmission as a function of both the voice signal and the data signal. Since the voice signal is effectively offset by the data signal, compandors normally found in the PSTN are not effective in improving the signal to noise ratio of the transmitted voice and data signal. Therefore, the voice signal is additionally companded in the transmitter before transmission over the PSTN. This additional companding by the transmitter improves the signal to noise ratio of the combined voice and data signal.

Abstract: A simultaneous voice and data (SVD) communications system includes an SVD modem at either endpoint of the system. Each SVD modem provides an SVD signal to the opposite endpoint, where this SVD signal includes both a voice channel and a data channel. One, or both, of these SVD modems allows the respective user to alter either the voice signal that is provided to that user, or the voice signal that is transmitted from that user, via the voice channel of the SVD signal, to the opposite SVD endpoint.

Abstract: A passive optical network architecture is disclosed for application in a local loop telephone environment. A local digital switch transmits an optical signal bearing information downstream over an optical fiber to the terminal equipment of a group of subscribers. This transmitted optical signal comprises light at a number of different wavelengths, i.e., it is a wavelength-division multiplexed signal, where each subscriber is associated with a particular wavelength of light. Each subscriber's terminal equipment detects that portion of the transmitted optical signal that exists at its assigned wavelength and thereby recovers the information sent by the local digital switch for that subscriber. However, a fraction of this detected optical signal is then remodulated by the subscriber's equipment with the subscriber's upstream information and returned to the local digital switch. As a result, no optical sources exist in the subscriber equipment in this optical network architecture.

Abstract: A low-voltage drop current regulator regulates the current in a data interchange circuit. In one embodiment, the low-voltage drop current regulator couples a positive power supply voltage to the power supply pin of a driver integrated circuit. In another form of the invention, the low-voltage drop current regulator is placed in series with the individual output leads of a driver integrated circuit to couple the respective output signals to respective pins of the data interchange circuit.

Abstract: In a wave solder manufacturing process, a test device is used to measure the contact-area between a solder wave and a printed wiring board. In particular, the test device is a printed wiring board (PWB) that includes at least two arrays of electrical contacts, one array near each side of the PWB. As the PWB makes contact with a solder wave, the number of electrical contacts in each array that are grounded by the solder wave are counted and displayed on an alpha-numeric display mounted on top of the PWB. This "distance-based" measurement provides an accurate determination of the uniformity of the contact-area, and concomitantly the dwell-time of the soldering process. This test device provides a basis for real-time adjustment of solder wave height, and end-to-end balance, in a solder wave machine. In particular a wave solder machine includes a means for receiving contact-area information from the test device and a means for adjusting the solder wave in response to the contact-area information.

Abstract: A "Personal Computer Memory Card International Association" (PCMCIA) peripheral, e.g., a modem, incorporates a shared memory interface to a personal computer. This shared memory interface provides the capability to easily program the PCMCIA peripheral either in the factory or in the field. In addition, the shared memory interface removes the requirement of having a resident "boot-up" code in the PCMCIA peripheral. Finally, the shared memory interface provides the capability to transfer user data from the personal computer, i.e., data terminal, to the PCMCIA modem at a higher data transfer rate than is currently available via the modem's universal asynchronous receive/transmit (UART) integrated circuit.

Abstract: In a wave solder manufacturing process, a test device is used to measure the contact-area between a solder wave and a printed wiring board. In particular, the test device is a printed wiring board (PWB) that includes at least two arrays of electrical contacts, one array near each side of the PWB. As the PWB makes contact with a solder wave, the number of electrical contacts in each array that are grounded by the solder wave are counted and displayed on an alpha-numeric display mounted on top of the PWB. This "distance-based" measurement provides an accurate determination of the uniformity of the contact-area, and concomitantly the dwell-time of the soldering process.

Abstract: A self-synchronizing scrambler/descrambler arrangement operates in two modes. In the first, or start-up mode, predetermined data is coupled to the scrambler and transmitted to the descrambler. This data is used to "seed", i.e., load, storage devices in the scrambler and descrambler with the same information. After a predetermined time interval, the start-up mode is terminated, and the scrambler and descrambler each operate in a steady-state mode. In this mode, the information loaded in the scrambler and descrambler devices are used to form the scrambler and descrambler key signals. Advantageously, in the steady-state mode, the occurrence of transmission errors does not effect the contents of the storage devices in the scrambler and descrambler. Hence, the prior art problem of error multiplication is avoided.

Abstract: A communications system simultaneously transmits both a primary data signal and a secondary voice signal in such a way that the dynamic range of the secondary voice signal is increased even though deliberate errors are introduced into the transmitted data portion of the signal. In particular, the communications system includes an error correcting technique like channel encoding and the constellation signal space is divided into a number of regions, where at least one of the regions overlaps with another region. The primary signal is channel encoded to select a particular one of the number of regions, the region being represented by a reference signal point value. The voice signal is encoded to provide a signal point vector, which is added to the reference signal point in such a way that the resultant signal point is located in the overlapping region thereby deliberately introducing an error into the resulting transmitted signal point stream.

Abstract: A simultaneous voice and data (SVD) modem is coupled to both a fax machine, which includes a fax modem, and a telephone set. When the fax machine initiates a fax-call, the SVD modem emulates signaling of the local loop. This allows the fax machine to operate without requiring modifications to the fax machine. After establishing a data connection with a far-end SVD modem, the near-end SVD modem demodulates the fax modulation signal from the fax machine to recover the fax data. The fax data is then re-modulated using a data modulation technique for transmission to the far-end SVD modem. The latter, demodulates the data portion of the signal to recover the fax data, which is then re-modulated using a fax modulation technique for transmission to a far-end fax machine.