Abstract: The system and method of the preferred embodiments may be directed to improving the signal-to-noise ratio in frequency spectrum regions where narrowband interference may be present. The system and method of the preferred embodiments includes reducing the narrowband interference by determining a noise estimate. In accordance with the noise estimate and output of a frequency domain equalizer, a noise-cancelled output may be obtained.

Abstract: A method is disclosed for signal detection in a wireless communication system that includes multiple-antenna arrays for transmission and reception. The method involves multiplying a vector of signals collected from respective receiving antennas by a nulling vector, such that the resulting vector product provides an estimated value corresponding to a specific one of the transmitted signals. A respective such multiplication is performed to detect each of the transmitted signals. In contrast to related methods of the prior art, each nulling vector is obtained from a channel matrix of estimated channel coefficients without performing any matrix inversion operations, and only a single pseudoinverse related to the channel matrix is computed. As a result, numerical stability is improved and the computational complexity of the method is reduced by an order of magnitude relative to methods of the prior art.

Abstract: A method and apparatus is provided that computes an optimal estimate of known clock frequency error between the transmitter and receiver using a known pilot signal and the statistics of the noise process. The estimate is computed such that the residual clock error is below the least count (the smallest frequency correction that can be imparted) of the VCXO that controls the receiver sample clock. A tracking technique based on a measure of drift in taps of frequency domain equalizers of different sub-carriers is disclosed. This tracking ensures that the residual mean square error is within a predefined bound. Finally, the least count effects in digitally controlled oscillators (DAC controlled VCXOs and Numerically Controlled Oscillators (NCXO)) are addressed by a dithering mechanism. The dithering mechanism involves imparting positive and negative clock corrections for different lengths of time in such a manner that the residual clock error becomes zero mean.

Abstract: A method for reducing interference combines soft symbols using existing processing devices. In particular, transmitted data signals are received over a plurality of paths. The received data signal includes an interference component. The received data signals are processed to provide a plurality of soft symbols that correspond to the transmitted data signal. The plurality of soft symbols are combined to reduce the interference component of the data signal and provided output signal that corresponds to the transmitted data signal. Accordingly, existing equalizers and combiners may be used to reduce interference. Related mobile user terminal and receivers are disclosed.

Abstract: A device for rapidly performing initial acquisition and frame synchronization of a received signal for a receiver in a CDMA communication system. To this end, the base station multiplies a spreading sequence for a pilot channel by a synchronization pattern which maintains a pattern of inverting its sign in order to delineate the boundaries of the short sequence periods. A mobile station initially calculates the spreading sequence of the short period and the correlation value to perform initial acquisition, and despreads N-chip duration around a boundary of the one short spreading sequence period to detect the multiplied pattern, thereby acquiring synchronization of a data frame.

Abstract: An impulse radio concurrently receives an impulse signal and interference. An interference sampler samples the interference before an expected time of arrival of an impulse in the impulse signal, to produce an interference nulling sample. Then, when the impulse arrives, a data sampler samples the impulse in the presence of the interference to produce a data sample including undesired interference energy. The anticipatory nulling sample is an estimate of the undesired interference energy captured in the subsequent data sample so that the nulling sample can be used to cancel the interference energy from the data sample. When the nulling sample precedes the data sample by an odd number of half cycle periods of the interference, the nulling sample is additively combined with the data sample to derive a corrected data sample, from which a portion of the interference energy is canceled.

Abstract: Joint channel estimation and maximum likelihood decoding method for Coded Orthogonal Frequency Division Multiplexing (COFDM) systems are presented. Using this method in conjunction with convolutional coding, robust and nearly optimal coherent detection can be achieved in rapid dispersive fading channels. Significant performance gain in packet data throughput is realized in a system with aggressive frequency reuse. A system for estimating channel characteristics in a multicarrier transmission system comprising means for receiving a multicarrier signal, means for applying Fast Fourier transformations to the multicarrier signal, means for estimating channel characteristics of a multicarrier channel over which the multicarrier signal was transmitted using iterative processing and means for decoding the transformed multicarrier signal is presented.

Abstract: A method of determining branch metric values in a detector. The method includes receiving a plurality of time variant signal samples, the signal samples having one of signal-dependent noise, correlated noise, and both signal dependent and correlated noise associated therewith. The method also includes selecting a branch metric function at a certain time index and applying the selected function to the signal samples to determine the metric values.

Abstract: To perform communication at a higher speed than in the past using a new communication device without giving influence on the existing slave communication device, on a master device of a communication system such as PHS, there are provided two series of modulators and demodulators for conventional speed and for higher speed, the two different speeds being changeable by a changeover switch. A slave device to be added newly is also designed in almost the same configuration. In the link setup phase, an information to request change of modulation method is notified together with a request of communication from the slave device to the master device. From the master device, an information to specify time slots to be used in the communication phase and an information to specify modulation method are notified to the slave device. In the communication phase, communication is performed using the modulation method and the time slots as specified.

Abstract: A method for reducing interference and a radio system where a signal spreadcoded by digital pseudo noise is used for communication are provided. As the delay distribution of the signals of subscriber terminal equipment at base stations is great and thus the mutual interference of the signals may also be great, the base station adjusts the phase of the spreading codes of the subscriber terminal equipment so as to reduce interference. The method and the radio system enable high data rates and reduce the calculation required for interference correction.

Abstract: A method for determining a frequency of a signal includes transforming the analog signal to the complex frequency range through a digital filtering, preferably a FFT, so that result vectors with amplitude and phase components are generated in the frequency range. As a result, a continuous sequence of transformation intervals (FFT intervals) develops within a measuring interval that can be predetermined. Subsequently, pairs of result vectors, which belong to the same predetermined frequency, are selected from predetermined transformation intervals (FFT intervals). Associated phase differences are then formed from which a weighted phase difference is determined. The weighted phase difference is used to correct the signal frequency determined from the amplitude spectrum. This method permits very accurate frequency measuring, especially for pulsed HF signals.

Abstract: A spread spectrum noise shaper uses a modulation technique to achieve a greater signal-to-noise or signal-to-interference ratio (SNR or SIR). The technique doubles the system SIR, in principle. This doubling yields a doubling in system capacity. SNR is increased by receiving the spread spectrum signal in the presence of less noise near the edge of the spread spectrum bandwidth. The technique requires only small additions to a conventional spread spectrum system, in the form of an extra modulator at the transmitter, and an extra demodulator and filter at the receiver.

Abstract: A method of detecting signals propagated on a carrier medium includes the step of determining a noise threshold level, relative to a noise floor on a carrier medium, such as for example POTS wiring. A peak threshold level is then determined relative to peaks of a data signal. A data threshold level is then calculated utilizing the noise threshold level and the peak threshold level. For example, the noise threshold level and the peak threshold level may be averaged to calculate the data threshold level. A data signal pulse is then detected on traversal of the data threshold level by the data signal.

Abstract: A measurement acquisition and display system generates graphical displays of Cumulative Distribution Function (CDF) peak-to-average power ratio measurements of a digitally modulated RF signal and an ideal digitally modulated RF signal, such as an 8-VSB digital television signal. A variable target operating point or planning factor value is enterable into the system that defines an operating point on the ideal CDF of peak-to-average power ratio display. The corresponding operating point on the RF signal CDF of peak-to-average power ratio display is determined and numerically displayed along with a numerical display of the difference between the ideal and real operating points. Alarm limit variables may be set for generating an alarm signal when the RF signal peak-to-average power ratio exceeds the alarm limits. The measurement acquisition and display system further generates a graphical display of channel frequency spectrum of the digitally modulated RF signal.

Abstract: A data transmission system, a receiver, and a recording medium in which a re-coder (16) generates pseudo transmission signals based on the virtual received data after a decoder (15) generates virtual received data based on virtual decision data from a virtual decision circuit (12), and a soft-decision circuit (18) outputs soft-decision data so as to decrease the number of different bits between the pseudo transmission signals and the received signals, and the received data are generated based on the soft-decision data.

Abstract: A bidirectional digital data communication system which generate phase coherent upstream clock and carrier signals from recovered downstream clock generated from a master clock in a central unit. The preferred species uses any downstream clock rate and generates a phase coherent upstream clock so long as the two clock rates can be related by the ratio M/N where M and N are integers. One embodiment uses an MCNS downstream and an SCDMA upstream and uses MNCN timestamp messages in the downstream to achieve an estimate of RU frame offset prior to establishing frame alignment using a ranging process. The use of timestamp messages to estimate the offset is aided by a low jitter method for inserting timestamp messages by avoiding straddling of MPEG packet headers with the sync message. Clock slip is detected by counting upstream clock cycles over a predetermined downstream clock interval and the RU transmitter is shut down if slip is detected to prevent ISI interference from misaligned codes.

Abstract: A repeater circuit (10) includes a decoder arrangement (34) and an encoder arrangement (33). The decoder arrangement (34) is connected to an input transmission line to receive an input encoded signal comprising a signal at one of four encoded voltage levels. Each of the four possible encoded voltage levels represents a different combination of first and second digital data signals. The decoder arrangement (34) decodes the input encoded signal to produce the first and second data signals. These first and second data signals then serve as inputs to the encoder (33) which encodes the signals into an output encoded signal. The output encoded signal comprises a signal similar to the input encoded signal but restored to account for parasitic resistance associated with the input transmission line (21).

Abstract: A method and apparatus for filtering an undesired ingress signal from an input signal. The apparatus includes an adaptive filter including an ingress synthesizer for recreating the undesired ingress signal and an ingress subtractor for subtracting the recreated ingress signal from the input signal. The ingress synthesizer includes a replica generator for generating replicas corresponding respectively to the input signal symbols, first summers for subtracting the replicas from the input signal for providing respective intermediate signals, second summers for subtracting a recreated ingress signal from the intermediate signals for providing respective error signals, a decision circuit for selecting the intermediate signal corresponding to the error signal having the smallest magnitude, and an ingress generator for processing the selected intermediate signal for providing the recreated ingress signal to the second summers and the ingress subtractor.

Abstract: A method and apparatus for transmitting and receiving acquired digital data over bandpass channels (i.e. channels having a limited range of frequencies) at high data transmission rates. Combined amplitude and phase modulation (quadrature amplitude modulation) is applied to the digital data and the sampled digital waveform converted to an analog waveform for passage over the bandpass channel. The sample rate is chosen as an integer multiple of the symbol rate and carrier frequency to significantly reduce processing overhead. Reception of the acquired data is similar to transmission and involves an analogous amplitude and phase demodulation. The quadrature amplitude modulation technique of the present invention is applied to an oil well-logging application to transmit the data acquired from the downhole logging instruments over the logging cable (bandpass channel) at high transmission rates.

Abstract: A system for sending sequences of data to be transmitted includes inputting data sequences to be transmitted and repeating data sequences to be transmitted. Data sequences referred to as "key sequences" which provide a key sequence for each data sequence to be transmitted coming from the input or from the repetition are selected independently of the data and the data sequence to be transmitted. The key sequences are different for data sequences to be transmitted which are separated by at least a predetermined number of other data sequences to be transmitted. Each data sequence to be transmitted is combined with the key sequence corresponding thereto in order to provide a sequence of processed data. Finally, frames successively representing each processed data sequence are sent.