Abstract: By teleconferencing participants (201-1-201-N.sub.1, 202-1-202-N.sub.2, 203-1-203-N.sub.3), who are grouped in diverse geographic locations with a multi-stage system, a significant improvement in the use of interexchange facilities is achieved. The signals transmitted by the telecommunications devices (e.g., telephones) of a group of conference participants located in the same general geographic area are inputted to a first stage bridge (210, 211, 212). Each first stage bridge measures the signal power of each signal and outputs on separate telephone circuits (218, 219, 220), a predetermined number of signals (for example, three) that have the highest signal power. These three signals are transmitted on the interexchange facilities (206) to a second stage bridge (216) to which similar groups of signals from other first stage bridges in other locations are also transmitted.

Abstract: A rotationally invariant, multilevel coded modulation scheme is provided by partitioning a constellation, such as an M-PSK or QAM constellation, into several trellis-subsets, each of which is further partitioned into block subsets. The input bits are then encoded to select a signal point from the constellation. A first portion of the input bits are differentially encoded. A second portion of the input bits, together with at least one of the differentially encoded bits, are trellis encoded to select a trellis subset of the constellation. A third portion of the input bits--excluding any differentially encoded bits --are block encoded to select a block subset from the selected trellis subset. A fourth portion of the input bits, together with the remaining differentially encoded bits, are used to select a signal point from the selected block subset.

Abstract: Digital signals, such as digitized television signals, are subjected to a source coding step followed by a channel mapping step. The source coding step causes the signal to be represented by first and second data streams. The first stream carries data regarded as more important and the second carries data regarded as less important. In the channel mapping step, the mapping is such that the data elements of the various data streams have differing probabilities of being erroneously detected at the receiver. The channel mapping step includes at least one multi-level coding step. The signal constellations used in the channel mapping step are partitioned into supersymbols, in which the distance between the symbols comprising at least ones of the supersymbols is less than a parameter referred to as the maximum intra-subset distance (MID).

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: Methods and apparatus for implementing intelligent work surfaces are provided. Work surfaces, such as desktops and floors, are covered with a tactile sensing array to provide tactile data to a processor. Regions on the sensing arrays may be defined to include predetermined sensing elements of the sensing array and may be specified to function as input devices, such as a keyboard, a mouse, or the like. Once defined, regions may be redefined to reposition a specified input device. Regions also may be respecified to function as a different input device. The arrays also may collect data at predetermined intervals for analysis, such as for identifying an individual or an object. For example, the force-image of an individual's handprint or footprint could be taken, analyzed, and compared against data representing the force-images of known individuals.

Abstract: An optical packet switch which receives data packets and switches those data packets in the optical domain without using recirculation devices is provided. The switch staggers the data packets in time to avoid packet collisions within the switch. The switch includes two stages that are coupled by optical delay lines. The non-blocking stages include a scheduling stage and a switching stage. Incoming data packets are received at the scheduling stage and are output to appropriate optical delay lines. The scheduling stage and the delay lines ensure that the data packets do not collide when the packets are switched at the switching stage of the optical switch.

Abstract: Telephone calls are directed from a first telecommunications platform to a second telecommunications platform, together with an identifier which uniquely identifies the call and enables telecommunication switches to monitor and maintain control over the call. The unique identifier enables the call to be returned from the second platform to the first platform. Once returned to the first platform, the call can be directed to a third telecommunications platform (and, subsequently, back to the first platform), without requiring the caller to place another call or to re-verify the caller's identity. The call identifier is used either to automatically return the call to the first platform after the occurrence of a predetermined event, or upon detecting predetermined, caller-dialed keystrokes indicating that the caller wishes to return to the interexchange carrier platform.

Abstract: Increased reliability for intelligent call processing systems is provided by collecting information from communications between the network database, the subscriber database, and the network switch. Message transfers between these network elements are monitored and correlated to identify those messages corresponding to a particular call. The messages for the call are analyzed to determine which database generated the instructions for routing the call. In particular, by comparing the routing number returned to the interexchange switch with the routing instruction information supplied by the subscriber's database, it can be determined whether the call was routed according to instructions from the subscriber's database.

Abstract: A high-speed information service system is provided which uses Primary Rate Interface (PRI) Integrated Services Digital Networks (ISDN) signaling and temporary, "out-of-band" signaling to improve information retrieval capability. ISDN signaling permits electronic addressing of information requested by the subscriber, thereby eliminating the delays which accompany DTMF signal processing. Communications between an information service provider and an individual information source are conducted using out-of-band signaling. That is, call setup and information request are processed using a channel other than the channel which carries data between the information service provider, the information source and the subscriber.

Abstract: A cost-effective, bandwidth-efficient, and power-efficient system is provided in which data streams received from several different video sources are converted into sequences of symbols selected from a predetermined constellation and are multiplexed on a symbol-by-symbol basis into a single sequence of symbols for transmission on a channel. Using a symbol multiplexer helps to mitigate the effect of bursty noise in the receiver and reduces the processing speed requirement in the receiver.

Abstract: A trellis-coded modulation system is provided in which the output of the trellis encoder is used to select a subset of a multidimensional QAM constellation. The selection process is performed such that a) the minimum square Euclidean distance between valid sequences of successive selected subsets is maximized, b) the resulting code is rotationally invariant, and c) the selected subset corresponding to a transition of the trellis encoder from a present state i to a different next state j is different from the selected subset that corresponds to a transition of the trellis encoder from a present state j to a next state i.

Abstract: An improved approximation of the desired codebook boundary is achieved, when quantizing data from a source with memory, by adding a dither sequence, the samples of which are contained within the Voronoi region of an unpartitioned lattice or the first level of lattice partitioning used to generate the trellis code. A sequence of data generated by the source with memory is quantized to a nearest sequence of a predetermined trellis code which is based on coset partitioning of a predetermined lattice into translates of a coset lattice. The trellis code sequence is then filtered with an inverse source filter. A dither sample is added to each sample of the sequence, such that (1) a sum of the dither sample and the filtered trellis code sequence sample lies on a super-lattice of the coset lattice, and (2) the dither sample is inside the Voronoi region of the super-lattice.

Abstract: The capacity of a multi-mode optical fiber system, such as a local area network, is increased by selectively propagating only higher-order modes through the multi-mode fiber. Because only a small number of higher-order modes are propagated, pulse spreading induced by modal dispersion is minimized, and the bandwidth of the multi-mode fiber is increased. Because of the reduced modal dispersion, higher-order modes are recovered from the multi-mode fiber in accordance with the invention without filtering the output of the fiber. This renders the system less vulnerable to mechanical perturbations that are known to reduce the bit error rate of systems requiring filtering. Thus, by propagating only higher-order modes in this manner, the "bandwidth-distance" product of the multi-mode fiber is significantly increased.

Abstract: Call setup time is reduced by automatically (1) identifying the type of signaling used by a caller to communicate with a central office, and (2) providing an indication of the signaling type to telephone switches or databases that will participate in routing and processing the telephone call. Dual Tone Multifrequency (DTMF) detectors located at a central office of a local exchange carrier detect whether a caller is using DTMF signaling. The local central office includes this information in a signaling message provided, for example, to interexchange carriers and other service providers which will use DTMF signaling during and after call setup. In this manner, the need to query the caller for this information is eliminated.

Abstract: Maximum operating speed is achieved in an array of memory cells by performing both read and write operations within a single memory cycle. As outgoing data are read from the memory cells, incoming data are stored immediately in those cells. Reduced power consumption is achieved in such memories by preventing the occurrance of a write operation if the value of a bit to be written to a memory cell is the same as the value of the bit currently stored in that memory cell. More particularly, the result of a read operation on a particular memory cell is compared with the data value to be written to that cell to determine whether a subsequent write operation is required. If the value in the cell equals the value to be written, the write operation is not performed.

Abstract: Transmission capacity of an optical fiber is increased by transmitting two optical signals of orthogonal polarizations through the fiber and distinguishing the signals from one another at the receiver by appropriately weighting polarization components representative of the transmitted signals. The weighted polarization components are summed to provide two output electrical signals that are proportional in magnitude to the two transmitted optical signals. Appropriate weighting of the signals eliminates cross-channel interference and maximizes the signal to noise ratio. Signals of arbitrary received polarizations are detected and separated from one another.

Abstract: In this invention, an optical beam is multiplexed with two independently generated electrical pulse signals applied simultaneously to an interferometer having at least two branches to perform electrical-to-optical operations, such as logic, encryption or multiplexing operations. A Y junction interferometer which is coupled to receive a CW or periodic occurring optical beam has at least one set of individually addressable contacts. A first pair of individually addressable contacts is coupled to receive a first independently generated electrical pulse signal of a given frequency and amplitude, and a second pair of individually addressable contacts coupled to the same or another branch of the Y is coupled to receive a second independently generated electrical pulse signal of a given frequency and amplitude which is other than substantially identical to and other than substantially in-phase inverse with the first signal.

Abstract: Arrays of light beams are combined in a manner that minimizes optical power loss by passing a first array of light beams through an angle-variant device onto a target surface while reflecting a second array of light beams off the angle-variant device onto the target surface. The light beams of the first array are arranged to strike the angle-variant device at a first family of angles at which the angle-variant device is substantially transmissive. The light beams of the second array are arranged to strike the angle-variant device at a second family of angles at which the angle-variant device is substantially reflective.

Abstract: The advantages of both active and passive modelocking techniques are realized within a single device by providing a p-i-n modulator formed at antiresonance within a Fabry-Perot etalon. The p-i-n modulator actively modulates light within the laser cavity by introducing periodic loss in response to changing voltages applied to the modulator. The p-i-n modulator includes an intrinsic region that is disposed between a p-doped region and an n-doped region. The modelocking performance of the p-i-n modulator is enhanced by the saturable absorber action of the intrinsic region.

Abstract: In a video telephony system, a coaxial cable network, which is preferably a part of an existing cable television system, provides a local link for the transmission of the video telephone signals between each originating and destination location and a respective "head end" located on the cable company premises. Each of the head ends is connected to a "point of presence" of a telephone interexchange carrier so that a connection between pairs of head ends, and thus between a pair of video telephone locations, can be made via a switched digital network maintained by the carrier. Certain of originating and destination locations comprise a standard television set, serving as the audio/video display, and a consumer-type camera or camcorder, serving as the audio/video source. Others of the originating and destination locations comprise ISDN video telephones which are connected to the various points of presence of the interexchange carrier via local exchange carrier telephone networks.