Abstract: The present invention provides a method and apparatus for enhancing and recognizing connected and degraded text. The enhancement process comprises filtering a scanned image to determine whether a binary image value of an image pixel should be complemented, determining whether complementing the value of the pixel reduces the sharpness of wedge-like figures in the image, and complementing the binary value of the pixel when doing so does not reduce sharpness. The recognition process may comprise determining primitive strokes in a scanned image, segmenting the scanned image into sub-character segments based on the primitive strokes, identifying features which characterize the sub-character segments, and comparing identified features to stochastic models of known characters and determining an optimum sequence of known characters based on the comparisons through the use of Viterbi scoring and level building procedures.

Abstract: Methods and apparatus are disclosed for improving the clarity and intelligibility of incoming speech in a telephone connection. Improved sound quality is provided by automatically selecting, or enabling the selection of, an appropriate sound enhancement for a particular individual at a given telephone number. Sound enhancements applied to calls originating from or terminating at a given telephone station are determined on a call-by-call basis. The sound enhancement set at the beginning of a telephone call can be changed mid-call to a different sound enhancement. Thus, different occupants of a household may select their own sound enhancement, or may select no enhancement at all.

Abstract: A method of coding a speech signal is described. In accordance with the method, a plurality of sets of indexed parameters are generated based on samples of the speech signal. Each set of indexed parameters corresponds to a waveform characterizing the speech signal at a discrete point in time. Parameters of the plurality of sets are grouped based on index value to form a first set of signals which represents the evolution of characterizing waveform shape; the signals of the first set are filtered to remove low frequency components and thereby produce a second set of signals which represents relatively high rates of evolution of characterizing waveform shape. The speech signal is then coded based on the second set of signals representing high rates of characterizing waveform shape evolution. Coding of the speech signal may further be based on a set of smoothed first signals.

Abstract: A speech coding method and apparatus which selectively applies speech coding techniques to time segments of speech information signals, such as, e.g., pitch cycle waveforms is disclosed. A speech information signal comprising N signal segments is coded with a first speech coder to provide a first coded representation for each of the N signal segments. A second speech information signal reflecting speech information not coded by the first coder is determined for each of one or more of the N signal segments. In addition to coding the N first speech information signal segments with the first speech coder, M of the second speech information signals are coded with a second speech coder, where 1.ltoreq.M.ltoreq.N-1. The selective coding of M of the second speech information signals is done responsive a coding criterion.

Abstract: Reliability of telephone service is increased by providing a test call apparatus configured to launch a test call to a preselected telephone number in response to a call from a remote location requesting that the test call be placed. The test call apparatus launches the test call as if the call were being made from the user-supplied originating area code, exchange, or phone number. The test call apparatus then bridges the requesting call and the test call to facilitate analysis of the routing of the test call.

Abstract: A method of coding a set of multi- level signals, such as video signals comprises filtering the set of multi-level signals into one or more sets of multi-level sub-band signals; allocating a first quantity of bits for use in coding a first set of sub-band signals; coding the first set of multi-level sub-band signals using zero or more of the first quantity of allocated bits; allocating a second quantity of bits for use in coding a second set of sub-band signals, the second quantity of bits comprising zero or more of the first quantity of bits not used in coding the first set of multi-level sub-band signals; and coding the second set of multi-level sub-band signals using zero or more of the second quantity of allocated bits. Three examples of the method am provided. A hardware implementation involving the use of digital signal processors operating in parallel is also provided.

Abstract: A method and apparatus providing antenna diversity is disclosed. A set of bits of a digital signal are used to generate a codeword of N symbols. Codewords are provided according to a channel code having a minimum Hamming distance, d.sub.min, where 2.ltoreq.d.sub.m .ltoreq.N. N signals representing N symbols of a codeword are transmitted with N different antennas. The N transmitted signals are received and isolated. A sequence of N received symbols is formed from the isolated symbols and compared with one or more valid codewords to associate the sequence with a codeword. A set of bits based on a codeword associated with the received sequence is generated.

Abstract: A model-based printing method and system for generating halftone output images corresponding to gray-scale-coded input signals. Models for individual two-level (e.g., black on white) printer types allow predicted printer error signals to be generated which can be used to modify the gray-scale coded signals in such manner as to produce binary signals which, when applied to the printer, create halftone images of enhanced quality. In an alternative embodiment binary signals are selected which minimize an error function based on the difference between (i) a predicted perceived image corresponding to the gray scale inputs as filtered by an eye-model filter and (ii) the halftone image resulting from filtering of the binary sequence by a filter modeling the printer followed by the eye-model filter.

Abstract: A model-based printing method and system for generating color halftone output images corresponding to color input signals. Models for individual printer types allow predicted printer error signals to be generated which can be used to modify the color signals in such manner as to produce output signals which, when applied to the printer, create color halftone images of enhanced quality. In an alternative embodiment, output image signals are selected which minimize an error function based on the difference between (i) a predicted perceived image corresponding to the color image input as filtered by an eye-model filter and (ii) the color halftone image resulting from filtering of the output image by a filter modeling the printer followed by the eye-model filter.

Abstract: The present invention is directed to a method of apparatus of enhancing the signal-to-noise ratio of a microphone array. The array includes a plurality of microphones and has a directivity pattern which is adjustable based on one or more parameters. The parameters are evaluated so as to realize an angular orientation of a directivity pattern null. This angular orientation of the directivity pattern null reduces microphone array output signal level. Parameter evaluation is performed under a constraint that the null be located within a predetermined region of space. Advantageously, the predetermined region of space is a region from which undesired acoustic energy is expected to impinge upon the array, and the angular orientation of a directivity pattern null substantially aligns with the angular orientation of undesired acoustic energy. Output signals of the array microphones are modified based on one or more evaluated parameters.

Abstract: A model-based printing method and system for generating halftone output images corresponding to gray-scale-coded input signals. Models for individual two-level (e.g., black on white) printer types allow predicted printer error signals to be generated which can be used to modify the gray-scale coded signals in such manner as to produce binary signals which, when applied to the printer, create halftone images of enhanced quality. In an alternative embodiment binary signals are selected which minimize an error function based on the difference between (i) a predicted perceived image corresponding to the gray scale inputs as filtered by an eye-model filter and (ii) the halftone image resulting from filtering of the binary sequence by a filter modeling the printer followed by the eye-model filter.

Abstract: A model-based printing method and system for generating halftone output images corresponding to gray-scale-coded input signals. Models for individual two-level (e.g., black on white) printer types allow predicted printer error signals to be generated which can be used to modify the gray-scale coded signals in such manner as to produce binary signals which, when applied to the printer, create halftone images of enhanced quality. In an alternative embodiment binary signals are selected which minimize an error function based on the difference between (i) a predicted perceived image corresponding to the gray scale inputs as filtered by an eye-model filter and (ii) the halftone image resulting from filtering of the binary sequence by a filter modeling the printer followed by the eye-model filter.

Abstract: A method of tailored error protection coding is disclosed. An illustrative coding method according to the present invention concerns encoding a first signal and a second signal to provide error protection for the signals, wherein the first signal requires greater error protection than the second signal. According to the method, the first signal is encoded with a first error protection code. The encoded first signal is then combined with the second signal. The combination of the encoded first signal and the second signal is further encoded with a second error protection code to generate a combined error protected signal, wherein the first signal is coded with both the first and second error protection codes. A second embodiment concerns the use of separate coders which apply different error protection codes to two signals. The two encoded signals are then combined into a single signal.

Abstract: A technique for reducing multiple access interference (MAI) experienced by receivers of transmissions from a transmitter, e.g., a base station, in a direct-sequence code division multiple access communication system, e.g., a cellular radio system, is disclosed. The technique provides for the precoding of user signature sequences for use in spreading information signals to be transmitted. The use of precoded signature sequences significantly reduces the average level of MAI experienced by the receivers. Despreading of received signals by receivers may be accomplished with the original (i.e., non-precoded) signature sequences. Thus, no changes to receivers are required. The technique includes a feature for determining a set of sequences for both transmitter and receiver from a smaller set of orthogonal sequences.

Abstract: The invention provides a method and apparatus for transmitting digital signal information to a receiver using a plurality of antennas. The invention involves applying a channel code to a digital signal producing one or more symbols. A plurality of symbol copies is made and each copy is weighted by a distinct time varying function. Each antenna transmits a signal based on one of the weighted symbol copies. Any channel code may be used with the invention, such as a convolutional channel code or block channel code. Weighting provided to symbol copies may involve application of an amplitude gain, phase shift, or both. The present invention may be used in combination with either or both conventional interleavers and constellation mappers.

Abstract: A security node disposed in the telecommunications network connecting calling and called parties transforms information (which can be voice, data, facsimile, video and other types of calls or messages) encrypted in a first format to (a) encrypted information in a different format or to (b) non-encrypted information, and vice-versa. The node is accessible from any location connected to the network. By routing calls or messages originated by the calling party and destined for the called party via the security node, and providing appropriate control signals to the node, the information may be encrypted only over a portion of the transmission path between the parties, and clear over the remainder of the transmission path. Alternatively, the information may be encrypted in different portions of the path using different encryption algorithms.

Abstract: A speech coding system robust to frame erasure (or packet loss) is described. Illustrative embodiments are directed to a modified version of CCITT standard G.728. In the event of frame erasure, vectors of an excitation signal are synthesized based on previously stored excitation signal vectors generated during non-erased frames. This synthesis differs for voiced and non-voiced speech. During erased frames, linear prediction filter coefficients are synthesized as a weighted extrapolation of a set of linear prediction filter coefficients determined during non-erased frames. The weighting factor is a number less than 1. This weighting accomplishes a bandwidth-expansion of peaks in the frequency response of a linear predictive filter. Computational complexity during erased frames is reduced through the elimination of certain computations needed during non-erased frames only.

Abstract: The present invention provides a method and apparatus for detecting control signal information for an element of a communication system. The control signal information is included in one or more segments of a signal communicated over a communication system channel. The invention provides for the application of a plurality of tapers to a segment of a communicated signal; the transformation of a tapered segment; the determination of a similarity score based on a transform of a tapered segment and a model of a control signal; the identification of control signal information based on a similarity score; and the creation of an indicator signal representative of the identified control signal information to the communication system element. The control signal information may comprise a dual-tone multi-frequency signal. The tapers may comprise a discrete prolate spheroidal sequence. A similarity score may be determined based on a ratio of energy distributions.

Abstract: A security node disposed in the telecommunications network connecting calling and called parties transforms information (which can be voice, data, facsimile, video and other types of calls or messages) encrypted in a first format to (a) encrypted information in a different format or to (b) non-encrypted information, and vice-versa. The node is accessible from any location connected to the network. By routing calls or messages originated by the calling party and destined for the called party via the security node, and providing appropriate control signals to the node, the information may be encrypted only over a portion of the transmission path between the parties, and clear over the remainder of the transmission path. Alternatively, the information may be encrypted in different portions of the path using different encryption algorithms.