Abstract: Interleaved block-coded modulation with built-in time diversity is used for fading channel applications. Various modulated block codes of various dimensionalities are disclosed, each built up from an M-DPSK constellation. The signal points making up each codeword are re-ordered by an interleaver in a way which matches the interleaving to the block code, thereby increasing the effective size of the interleaver.

Abstract: Primary and secondary data are communicated from a transmitter to a receiver in a communication system. The value of an individual primary data word is communicated by transmitting an individual one of first plurality of channel symbols associated with that value while the value of a combined data word comprising an individual primary data word and an individual secondary data word is communicated by transmitting an individual one of second plurality of channel symbols associated with that value. In the receiver, both the primary and secondary data word values are recovered from the channel symbols thus transmitted. The approach of alternating two sets of channel symbols for transmission depending on the data word size can further apply to data communications at various fallback speeds.

Abstract: A signal coding technique for use with fractional bit rates is disclosed which, for a given dimensionality, allows the use of smaller constellations, and thus provides greater robustness in the presence of various impairments, than would otherwise be the case yet entails essentially no decoding delay penalty. In this technique, one or more of the input bits are trellis encoded and the trellis-encoded bits identify one of a predetermined plurality of subsets of the signal constellation and the particular symbols selected for transmission from two or more identified subsets are chosen by the non-trellis-encoded bits interdependently.

Abstract: In a trellis coding arrangement, the alphabet is comprised of a plurality of cosets of a sublattice of a p-dimensional lattice, where p<4.

Abstract: In a private telecommunications network, a plurality of digital PBXs are interconnected via pairs of codecs. The codecs of each pair, or "tandem", are each operative to encode 64 kilobit/second (kbps) mu-law speech so as to compress it to 16 kbps speech for transmission to the other codec in the tandem. The latter is operative to thereafter decompress the 16 kbps speech back to 64 kbps. Each codec has a second mode of operation in which, rather than decode the encoded speech, it preserves the bits thereof in its own output signal. The codec transitions to this mode whenever it recognizes the presence of another codec on its high-bit-rate side of the connection. As a result, only one encoding/decoding cycle is performed across the connection, thereby minimizing the speech-coding-induced distortion and delay therein.

Abstract: In a telephone local loop transmission arrangement, data is communicated from the customer premises to the central office utilizing a multi-dimensional, passband signal illustratively at 480 kb/s and 1.544 Mb/s.

Abstract: In a data transmission system using a predetermined trellis code, the output signal points are selected from a predetermined alphabet representing (k+n)-bit input words by using the values of n bits of each input word, and bits from previous input words, to identify a particular one of 2.sup.m subsets of the signaling alphabet m>n. The other k bits of the input word identify an ensemble of four signal points of the identified subset. This ensemble is characterized by having a first signal point whose odd components and even components each sum to a value no less than zero, a second signal point whose odd components sum to a value no less than zero and even components a value no greater than zero, a third signal point whose odd components sum to a value no greater than zero and even components a value no less than zero, and a fourth signal point whose odd components and even components each sum to a value no greater than zero.

Abstract: In a voiceband data multipoint network, each tributary modem transmits, in a trailer which follows the user data, a tributary modem identification, a sequence number which advances for each start-up and a checksum. The observation at the receiver of a gap in the series of sequence numbers in messages determined to have originated from a particular tributary modem is used to accurately compute a missed message rate for that modem.

Abstract: Modems, data service units, application modules and other data communication devices, installed in a common equipment cabinet, are interconnected by way of a time division multiplexed bus. Time slots assigned to the various devices recur at a number of rigidly-spaced access periods across each time division multiplex frame. The rate at which the access periods occur and the total number of access periods that make up each frame are chosen in such a way as to accomodate a mix of devices having respective bus access rates wherein there is at least one pair of rates for which neither rate of the pair is a multiple of the other. The process of allocating access periods to the time slots is carried out using a known lemma to identify linear Diophantine equation solutions.

Abstract: A redundant (multiple) bus system for interconnecting a plurality of data source and destination entities and arranged to direct data communications over an alternative bus in the event that a prior call to a destination over a first bus was unsuccessful. Each source entity maintains a table designating a separate logical path over each bus to each destination entity, marking each path designation in accordance with the success or failure of calls directed through the path. The bus selection for delivering a communication to any destination is determined in accordance with designation markings for the paths to the destination and independent of designation markings for paths to other destinations whereby a bus may be selected for a delivery to one destination even though prior deliveries over the bus to other destinations have failed.

Abstract: In a voiceband data multipoint network, each tributary modem transmits, in a trailer which follows the user data, a tributary modem identification, a sequence number which advances for each start-up and a checksum. The observation at the receiver of a gap in the series of sequence numbers in messages determined to have originated from a particular tributary modem is used to accurately compute a missed message rate for that modem.

Abstract: Modems, data service units, application modules and other data communication devices, installed in a common equipment cabinet, are interconnected by way of a time division multiplexed bus. Time slots assigned to the various devices recur at a number of regularly-spaced access periods across each time division multiplex frame. The rate at which the access periods occur and the total number of access periods that make up each frame are chosen in such a way as to accommodate a mix of devices having respective bus access rates wherein there is at least one pair of rates for which neither rate of the pair is a whole number multiple of the other. The process of allocating access periods to the time slots is carried out using a known lemma to identify linear Diophantine equation solutions.

Abstract: In a data transmission system using a predetermined trellis code, the output signal points are selected from a predetermined alphabet representing (k+n)-bit input words by using the values of n bits of each input word, and bits from previous input words, to identify a particular one of 2.sup.m subsets of the signaling alphabet m>n. The other k bits of the input word identify a pair of signal points of the identified subset. The sum of the components of one point of each pair is no less than zero and the sum of the components of the other point of that pair is no greater than zero. A running sum of the components of the signal points previously generated is maintained. If at any point in time the running sum is greater than zero, the signal point of the identified pair whose component sum is no greater than zero is generated, and vice versa. This scheme provides a channel-coded signal having a spectral null at dc.

Abstract: In accordance with the present invention, local loop testing in an echo canceller based modem is provided in a manner in which proper operation of both the receiver and echo canceller can be assessed simultaneously. Specifically, the modem includes means for generating data and interfering symbol sequences and for applying the interfering sequence to both the echo canceller and the modem transmitter, while applying the data sequence only to either the transmitter or the echo canceller. During closed loop testing, the modem connection to the transmission line is opened, and a portion of the output of the modem transmitter is applied to the modem receiver via a leakage path through the hybrid. The received symbol is subtracted from the echo canceller output, resulting in application to the receiver of only a version of the data symbol sequence. Advanced knowledge of the characteristics of the data symbol sequence allows proper receiver operation to be verified.

Abstract: In a data receiver employing a fractionally spaced equalizer, the phase with which samples of the received signal are formed is controlled in response to a signal indicative of the center of gravity of the equalizer coefficient.

Abstract: Users of an on-line documentation facility in a computer system are provided with the capability of specifying modifications to be made to the documentation that would otherwise be provided by the system.

Abstract: A voiceband data signal comprised of frequency-division-multiplexed primary and secondary channels is applied to the receiver portion of a modem. Circuitry within the modem for recovering the primary channel data includes an anti-aliasing filter, A/D converter, Hilbert filter, demodulator, fractionally-spaced equalizer, carrier recovery circuit and decision circuit. An error signal put out by the decision circuit is used by the equalizer to update its coefficients, and thus its transfer function. Rather than using a bandpass filter to remove the secondary channel energy prior to sampling and equalization, the receiver relies on the fractionally-spaced equalizer to suppress the secondary channel energy.

Abstract: A stream of binary bits is converted into blocks of eight parallel bits. A first group of five of the eight bits addresses a memory device which has thirty-two code words each having four numbers representing the coordinates of signal points in four-dimensional space. The remaining three of the eight bits are expanded to four bits by a convolutional encoder having three bits of memory. These four bits are then used to multiply the four numbers of a code word read out from the memory device. This method permits a block of eight binary bits to be coded into any one of five hundred and twelve four-dimensional code words.

Abstract: A voiceband data set network includes a control data set (10), a plurality of tributary data sets (4a, 4b . . . 4n) and a diagnostic control device (5). User-provided data is communicated between the control data set and the tributary data sets via a primary channel within a four-wire private telephone line (11, 12). Diagnostic and control information is communicated between the control data set and the tributaries via a secondary channel within the private line. Diagnostic and control information is communicated between the diagnostic control device and the control data set, with which it is co-located, via a control channel. Each data set includes a data set diagnostic unit (50), or DDU, via which it transmits and receives the diagnostic and control information.

Abstract: A full duplex, synchronous data set (10) includes primary signal processing circuitry which generates a modulated transmit data signal in response to serial data from a terminal interface (17). The modulated data signal is transmitted over a primary channel of a transmit line (11). The primary signal processing circuitry also receives modulated data signals from a primary channel of a receive line (12) and recovers therefrom a serial bit stream for presentation to the interface. The operating parameters of the primary signal processing circuitry are specified by a primary controller (30) over a plurality of buses (PA, PC, PD). The primary controller includes a microprocessor (310) and associated peripherals (315, 320, 325, 330, 335). The data set also includes secondary signal processing circuitry (40) which transmits and receives diagnostic and control information over respective secondary channels of the transmit line and receive lines.