Abstract: A generalized form of a multimodulus algorithm (GMMA) is described for use in blind equalization. A receiver uses a signal point constellation representing 256 levels. This signal space is divided into sample, or data, subsets. Cost function minimization is done with respect to each sample subset.

Abstract: A distributed processing telephone system for providing "plug-and-play" capability. In particular, a key telephone system comprises a plurality of telephone sets. Each telephone set is coupled to a least one common communications channel, or telephone line, and includes at least one tunable RF modem. There is no key service unit (KSU). That is, the system is KSU-less. Resources of the telephone system are allocated using a peer-to-peer protocol. For example, as each telephone set is newly added to the system, the new telephone set adaptively determines its own allocation of resources, e.g., intercom numbers, etc. During operation, each telephone set requests the appropriate resources from its peers.

Abstract: A distributed processing telephone system for providing "plug-and-play" capability. In particular, a key telephone system comprises a plurality of telephone sets. Each telephone set is coupled to at least one common communications channel, or telephone line, and includes at least one tunable RF modem. There is no key service unit (KSU). That is, the system is KSU-less. Resources of the telephone system are allocated using a peer-to-peer protocol. For example, as each telephone set is newly added to the system, the new telephone set adaptively determines its own allocation of resources, e.g., intercom numbers, etc. During operation, each telephone set requests the appropriate resources from its peers.

Abstract: In an embodiment of the invention, a speaker/microphone peripheral 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, when headphones are inserted or removed, the acoustic echo canceler is reset.

Abstract: A blind equalization cost function called the "constrained Hilbert cost function" (CHCF) provides for reliable blind convergence of a two-filter equalizer structure. In particular, the CHCF cost function is designed in such a way that the two filters are constrained to be a Hilbert pair. Advantageously, this technique can be used with any blind equalization algorithms, such as RCA, CMA, and MMA.

Abstract: A digital audio broadcasting (DAB) system includes a radio-frequency (RF) transmitter and a corresponding RF receiver. The RF transmitter transmits an RF DAB signal that includes a pilot signal at 250 Khz. An RF section of the RF receiver includes a phase-lock-loop (PLL) to compensate for any carrier frequency differences in the received RF DAB signal. This PLL tracks the phase of the received RF DAB signal when an amplitude of a recovered IF signal is above a predetermined threshold and upon detection of the pilot signal.

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 in 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 system incorporates a perceptual audio coder that encodes a digital audio signal for broadcast. A "source label" is provided by controlling the perceptual audio coder in such a way that the number of coefficient samples, n, used in each transmission frame represents information about the source. For example, if the value of n is odd, then a binary "1" is transmitted, but if the value of n is even, then a binary "0" is transmitted. As a result, a low-bit rate "source label" is transmitted over a number of frames. In a receiver, the source of the digital audio signal is identified by simply monitoring the value of n over the number of frames. More importantly, the value of n in each frame is required by a corresponding perceptual audio decoder, in the receiver, to correctly recover the digital audio signal.

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.