Abstract: A method and apparatus for reducing after images in motion video display. In the present invention, an intensity scaled image of a previous frame or set of frames is subtracted from the present frame before displaying the present frame. In the exemplary embodiment, the scaling factor is determined by measuring the intensity of the after image for the display device. In a preferred embodiment, the after image reduction system of the present invention takes into account the nonlinearities of the display device. That is the nonlinear relationship between the voltage applied to a display device and the intensity of the resulting display.

Abstract: A method for controlling echo canceling in an echo cancellation system using a state machine controller. A far-end speech signal transmitted through a communications channel may be passed through an echo channel to produce an echo signal. The echo signal is summed with a near-end speech signal and transmitted back to the far-end. An echo canceller rejects the echo signal by forming an estimate of the echo signal and subtracting the estimate from the sum of the near-end speech signal and the echo signal. The echo canceller includes a state machine which is configured into a predetermined state of a plurality of states depending on the presence near-end speech signal, far-end speech signal, or both near-end and far-end speech signals. Based on the predetermined state of the state machine, the controller in the state machine controls the update of coefficients of a plurality of adaptive filters.

Abstract: A method and apparatus for detecting and correcting for variations in the flat delay, which permits smooth echo canceller operation even under dynamic delay conditions. In a delay monitor, the received signal is compared against delayed versions of the echo estimate to determine whether a shift in the echo delay has occurred. If such a shift in delay has occurred then a signal indicating the amount of the shift is to the adaptive filter of the echo canceller and the filter taps are updated in accordance with the delay shift value.

Abstract: A method and system, for use in a communication system in which data is transmitted in data frames of a predetermined time duration, for the positioning of the data within the data frames for transmission. A computation circuit computes according to the deterministic code a pseudorandom position for the data within each data frame. A positioning circuit positions the data within each data frame in the computed position.

Abstract: An apparatus and method for performing speech signal compression, by variable rate coding of frames of digitized speech samples. The level of speech activity for each frame of digitized speech samples is determined and an output data packet rate is selected from a set of rates based upon the determined level of frame speech activity. A lowest rate of the set of rates corresponds to a detected minimum level of speech activity, such as background noise or pauses in speech, while a highest rate corresponds to a detected maximum level of speech activity, such as active vocalization. Each frame is then coded according to a predetermined coding format for the selected rate wherein each rate has a corresponding number of bits representative of the coded frame. A data packet is provided for each coded frame with each output data packet of a bit rate corresponding to the selected rate.

Abstract: A noise replacement system and method for providing a synthesized noise replacement signal to an output speech channel in an echo cancellation system. A far-end speech signal transmitted through a communications channel may be passed through an echo channel to produce an echo signal. The echo signal is summed with near-end speech and transmitted back to the far-end in the output speech channel. An echo canceller rejects the echo signal by forming an estimate of the echo signal and subtracting the estimate from the sum of the near-end speech and the echo signal to produce an echo residual signal. When only the far-end speaker is talking, the echo is completely rejected by replacing the echo residual signal with a synthesized noise signal. The noise is synthesized to match the power and spectral characteristics of the actual background noise at the near-end to prevent the far-end speaker from detecting any change in signal characteristics.

Abstract: A method and apparatus for performing subband adaptive filtering is proposed. A signal is prefiltered by a set of complementary filters to provide corresponding subbands of the input signal. The subbands of the signal are then provided to adaptive filters that filter the subbands separately. The individually filtered subbands are then summed. In an exemplary implementation an echo canceller is presented which employs the subband filtering method and apparatus.

Abstract: A novel an improved method of acquisition in a spread spectrum communication system is presented. In the present invention, a large window of PN chip offset hypotheses are searched and if an energy signal is found that might indicate the presence of the pilot signal having one of the chip offsets of the large search window, then a search of a subset of offset hypotheses, or small window, is searched.

Abstract: A method and apparatus for negotiating service configuration in a digital communication system is disclosed. In an exemplary embodiment the service negotiation system is implemented in a wireless spread spectrum communication system. The service configuration comprises data rates, frame formats and types of services. Types of service may include speech encoding, facsimile or digital data services. Further described herein is a digital transmitter and receiver using the service negotiation system to provide service configuration mutually acceptable at both ends of a communication link.

Abstract: An encoder for encoding data as trellis coded data and a decoder for decoding the trellis coded data. The encoder uses a rate 1/2 convolutional encoder punctured to a rate k/n to produce n symbols from k input bits. The symbols are converted by a converter to sets of p symbols and provided to an interleaver. In the interleaver certain ones of the symbols are delayed. Symbol sets are output from the interleaver to a 2.sup.P -ary modem for modulation and transmission. The decoder uses a modem for providing from the modulated data sets of p symbols. A deinterleaver delays certain ones of the symbols to achieve time alignment of the originally interleaved symbols. The sets of time aligned symbols are provided to metric calculators for computing signal metrics which are provided to a converter for providing n sets of metrics to a metric decoder. The metric decoder computes from the n sets of metrics an estimate of the encoded k data bits.

Abstract: A system and method for adaptively sectorizing channel resources within a digital cellular communication system is disclosed herein. The system includes an antenna arrangement for providing at least first and second electromagnetic beams for receiving a first information signal transmitted by a specific one of a plurality of users, thereby generating first and second received signals. A first set of beam-forming signals are then generated from the first and second received signals. A demodulating receiver is provided for demodulating at least first and second beam-forming signals included within the first set of beam-forming signals, thereby producing first and second demodulated signals. The system further includes a tracking network for tracking multipath information signals, received from various positions and angles of incidence, based on comparison of the first and second demodulated signals.

Abstract: A linear coverage area antenna system for use within a CDMA communication system is described. In a preferred implementation, two linear coverage area antenna structures are positioned in parallel and coupled to a base station. Within the base station, a transmitter generates remote user directed spread spectrum signals, these signals being provided to the first and second linear coverage area antenna structures through an antenna interface. The antenna interface includes a time delay element for introducing a predetermined time delay between components of the remote user directed spread spectrum signals transmitted by the first and second linear coverage area antenna structures, respectively.

Abstract: A method and system by which parameter data representative of vocoded speech are organized into a data packet for transmission so as to reduce the impact of transmission channel induced errors on the data packet. A data packet is constructed with certain most perceptually significant bits of parameter data at the beginning of the data packet. Following in the data packet are lesser perceptually significant bits of the same parameter data. Other parameter data then follows in the data packet. Interleaved in the data packet following the most perceptually significant bits at the beginning of the data packet are most perceptually significant bits of other parameter data. A parity check code is computed from the most perceptually significant bits in the data packet and also interleaved in the data packet following the most perceptually significant bits at the beginning of the data packet.

Abstract: A system and method for detecting convergence in an echo canceller prevent false convergence from occurring as a result of receiving only tones in an input signal. An adaptive filter is used in an echo canceller to estimate an echo signal produced by an unknown echo channel. The estimated echo signal is subtracted from the return signal to remove the echo produced by the unknown echo channel. To prevent the echo canceller from falsely converging on a signal which contains only tones a system and method are provided for detecting the presence of tones in the absence of other frequencies. Filter taps of the adaptive filter are filtered to produce a filtered signal. The amount of energy in the filtered signal is compared to the amount of energy in the unfiltered filter taps to determine whether only tones have been present. If only tones have been present, the echo canceller is not allowed to reduce the adaptation step size of the adaptive filter.

Abstract: A video compression system and method for compressing video data for transmission or storage by reducing the temporal redundancy in the video data is described. A frame of video data is divided into a variable number of blocks of pixel data of varying size, and each block of data is compared to a window of pixel data in a reference frame of pixel data, typically the previous frame. A best matched block of pixel data is selected from the window of pixel data in the reference frame, and a displacement vector is assigned to describe the selected block location in the reference frame relative to the current block of pixel data. The number and size of the blocks of pixel data are permitted to vary, in order to adapt to motion discontinuities in the sequential frames of pixel data.

Abstract: An improved method and system for performing a pilot signal searching operation in anticipation of handoff in mobile station communication between base stations is disclosed herein. The searching operation is described herein as being implemented within a cellular communication system which uses code division multiple access (CDMA) modulation techniques. The mobile station maintains a list of an Active Set of pilot signals transmitted from base stations with which the mobile station is to communicate through, and a Neighbor Set of pilots from base stations within a predetermined proximity of the mobile station. In addition to the Neighbor and Active Sets of pilots, the mobile station maintains a list of Candidate and Pre-Candidate Sets of pilots. Based on analysis of the signal strength of the pilot signals received at the mobile station, base station entries from the Neighbor Set may be assigned to the Pre-Candidate and Candidate Sets, and eventually to the Active set.

Abstract: A method and apparatus for arranging various types of data, and at various rates, into a uniquely structured format for transmission. Data for transmission formatting may be vocoder data or different types of non-vocoder data. The data organized into frames of a predetermined time duration for transmission. The data frames are organized, depending on the data, to be at one of several data rates. Vocoder data is provided at one of several data rates and is organized in the frame according to a predetermined format. Frames may be formatted with a sharing of vocoder data with non-vocoder data to be at a highest frame data rate. Different types of non-vocoder data may be organized so as to also be at the highest frame data rate. Additional control data may be provided within the data frames to support various aspects of the transmission and recovery upon reception.

Abstract: A method and apparatus are provided for performing a Hadamard transform operation. The basic building block of the apparatus is an FHT engine having a difference circuit for subtracting the input symbol from a delayed processed symbol, first multiplexer for providing either the difference of the delayed processed symbol and the input symbol or the input symbol, a summing circuit for adding the input symbol to the delayed processed symbol and a second multiplexer for providing either the sum of the input and the delayed processed symbol or the delayed processed symbol as an output. This basic engine is designed to work in conjunction with a variety of different memory configurations. The engines can then be placed in series to perform a Hadamard transform of all defined orders. In addition, two methods of optimizing the use of memory resources are described. On involves the optimal configuration of the memory elements and the second involves truncation.

Abstract: An echo canceller and method for cancelling in a return channel signal an echoed receive channel signal where the echoed receive channel signal is combined by an echo channel with an input return channel signal. The echo canceller has a first filter which generates first filter coefficients, generates a first echo estimate signal with the first filter coefficients, and updates the first filter coefficients in response to a first filter control signal. A first summer subtracts the first echo estimate signal from a combined return channel and echo receive channel signal to generate a first echo residual signal. A second filter generates second filter coeffidents, generates a second echo estimate signal with the second filter coefficients, and updates the second filter coefficients in response to a second filter control signal.

Abstract: An apparatus that automatically adjusts the adaptation block size for a least-mean square (LMS) adaptive filter depending on the input signal-to-noise ratio (SNR) is disclosed. The apparatus monitors the instantaneous SNR and continually adjusts the block size to provide high noise immunity, thereby increasing the convergence speed of the filter and decreasing the asymptotic mean-square error. An exemplary embodiment of the present invention is presented in the context of acoustic echo cancellation, though it is noted that the adaptive filter of the present invention is useful in any environment in which the noise characteristics are subject to change.